drm/amdgpu/virt: add wait_reset virt ops

Driver can use this interface to check if there's a function level
reset done in hypervisor. It's helpful when IRQ handler for reset
is not ready, or special handling is required.

Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Monk Liu <monk.liu@amd.com>
Signed-off-by: pding <Pixel.Ding@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>