drm/amdgpu: Differentiate between Raven2 and Raven/Picasso according to revision id

Due to the raven2 and raven/picasso maybe have the same GC_HWIP version.
So differentiate them by revision id.

Signed-off-by: shanshengwang <shansheng.wang@amd.com>
Signed-off-by: Jesse Zhang <Jesse.Zhang@amd.com>
Acked-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>