arm64: rsi: use linear-map alias for realm config buffer

rsi_get_realm_config() passes its argument to virt_to_phys(), but
&config is a kernel image address and not a linear-map alias.
On arm64 this triggers the below warning:

virt_to_phys used for non-linear address: (____ptrval____) (config+0x0/0x1000)
WARNING: arch/arm64/mm/physaddr.c:15 at __virt_to_phys+0x50/0x70, CPU#0: swapper/0
Modules linked in:
.....
Hardware name: linux,dummy-virt (DT)
pstate: 200000c5 (nzCv daIF -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : __virt_to_phys+0x50/0x70
lr : __virt_to_phys+0x4c/0x70
.....
......
Call trace:
__virt_to_phys+0x50/0x70 (P)
arm64_rsi_init+0xa0/0x1b8
setup_arch+0x13c/0x1a0
start_kernel+0x68/0x398
__primary_switched+0x88/0x90

Pass lm_alias(&config) instead so the RSI call uses the linear-map
alias of the same buffer and avoids the boot-time warning.

Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>