Support GFX soft reset for gfx v11.

V3: use ib test check soft reset.
V4: squash in unused variable fix (Alex)
Signed-off-by: Likun Gao <Likun.Gao@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>