drm/amdgpu: fix fence fallback timer expired error

IH is not working after switching a new gpu index for the first time.

During VM resume, QEMU programming of VF MSIX table (register GFXMSIX_VECT0_ADDR_LO)
may not work.The access could be blocked by nBIF protection as VF isn't in
exclusive access mode. Exclusive access is enabled now, disable/enable MSIX
so that QEMU reprograms MSIX table.

call amdgpu_restore_msix on resume to restore msix table.

Signed-off-by: Samuel Zhang <guoqing.zhang@amd.com>
Acked-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>