vfio/xe: Reorganize the init to decouple migration from reset

Attempting to issue reset on VF devices that don't support migration
leads to the following:

BUG: unable to handle page fault for address: 00000000000011f8
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 0 P4D 0
Oops: Oops: 0000 [#1] SMP NOPTI
CPU: 2 UID: 0 PID: 7443 Comm: xe_sriov_flr Tainted: G S U 7.0.0-rc1-lgci-xe-xe-4588-cec43d5c2696af219-nodebug+ #1 PREEMPT(lazy)
Tainted: [S]=CPU_OUT_OF_SPEC, [U]=USER
Hardware name: Intel Corporation Alder Lake Client Platform/AlderLake-P DDR4 RVP, BIOS RPLPFWI1.R00.4035.A00.2301200723 01/20/2023
RIP: 0010:xe_sriov_vfio_wait_flr_done+0xc/0x80 [xe]
Code: ff c3 cc cc cc cc 0f 1f 84 00 00 00 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 0f 1f 44 00 00 55 48 89 e5 41 54 53 <83> bf f8 11 00 00 02 75 61 41 89 f4 85 f6 74 52 48 8b 47 08 48 89
RSP: 0018:ffffc9000f7c39b8 EFLAGS: 00010202
RAX: ffffffffa04d8660 RBX: ffff88813e3e4000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc9000f7c39c8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff888101a48800
R13: ffff88813e3e4150 R14: ffff888130d0d008 R15: ffff88813e3e40d0
FS: 00007877d3d0d940(0000) GS:ffff88890b6d3000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000000011f8 CR3: 000000015a762000 CR4: 0000000000f52ef0
PKRU: 55555554
Call Trace:
<TASK>
xe_vfio_pci_reset_done+0x49/0x120 [xe_vfio_pci]
pci_dev_restore+0x3b/0x80
pci_reset_function+0x109/0x140
reset_store+0x5c/0xb0
dev_attr_store+0x17/0x40
sysfs_kf_write+0x72/0x90
kernfs_fop_write_iter+0x161/0x1f0
vfs_write+0x261/0x440
ksys_write+0x69/0xf0
__x64_sys_write+0x19/0x30
x64_sys_call+0x259/0x26e0
do_syscall_64+0xcb/0x1500
? __fput+0x1a2/0x2d0
? fput_close_sync+0x3d/0xa0
? __x64_sys_close+0x3e/0x90
? x64_sys_call+0x1b7c/0x26e0
? do_syscall_64+0x109/0x1500
? __task_pid_nr_ns+0x68/0x100
? __do_sys_getpid+0x1d/0x30
? x64_sys_call+0x10b5/0x26e0
? do_syscall_64+0x109/0x1500
? putname+0x41/0x90
? do_faccessat+0x1e8/0x300
? __x64_sys_access+0x1c/0x30
? x64_sys_call+0x1822/0x26e0
? do_syscall_64+0x109/0x1500
? tick_program_event+0x43/0xa0
? hrtimer_interrupt+0x126/0x260
? irqentry_exit+0xb2/0x710
entry_SYSCALL_64_after_hwframe+0x76/0x7e
RIP: 0033:0x7877d5f1c5a4
Code: c7 00 16 00 00 00 b8 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 f3 0f 1e fa 80 3d a5 ea 0e 00 00 74 13 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 54 c3 0f 1f 00 55 48 89 e5 48 83 ec 20 48 89
RSP: 002b:00007fff48e5f908 EFLAGS: 00000202 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007877d5f1c5a4
RDX: 0000000000000001 RSI: 00007877d621b0c9 RDI: 0000000000000009
RBP: 0000000000000001 R08: 00005fb49113b010 R09: 0000000000000007
R10: 0000000000000000 R11: 0000000000000202 R12: 00007877d621b0c9
R13: 0000000000000009 R14: 00007fff48e5fac0 R15: 00007fff48e5fac0
</TASK>

This is caused by the fact that some of the xe_vfio_pci_core_device
members needed for handling reset are only initialized as part of
migration init.

Fix the problem by reorganizing the code to decouple VF init from
migration init.

Fixes: 1f5556ec8b9ef ("vfio/xe: Add device specific vfio_pci driver variant for Intel graphics")
Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/work_items/7352
Cc: stable@vger.kernel.org
Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Link: https://lore.kernel.org/r/20260410224948.900550-1-michal.winiarski@intel.com
Signed-off-by: Alex Williamson <alex@shazbot.org>