drm/amdkfd: Clear VRAM on allocation to prevent stale data exposure

KFD VRAM allocations set AMDGPU_GEM_CREATE_VRAM_WIPE_ON_RELEASE
but not AMDGPU_GEM_CREATE_VRAM_CLEARED, leaving freshly allocated
VRAM with stale data from prior use observable by compute kernels.

The GEM ioctl path already sets VRAM_CLEARED for all userspace
allocations via amdgpu_gem_create_ioctl() and
amdgpu_mode_dumb_create(). The KFD path was missing this flag,
allowing stale page table remnants to leak into user buffers.

This causes crashes in RCCL P2P transport where non-zero data in
ptrExchange/head/tail fields corrupts the protocol handshake.

Signed-off-by: Amir Shetaia <Amir.Shetaia@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org