drm/amdgpu: add mmhub v1_8_0 ip headers

Add mmhub v1_8_0 register offset and shift masks
header files

v2: update headers (Alex)

Signed-off-by: Hawking Zhang <Hawking.Zhang@amd.com>
Reviewed-by: Le Ma <Le.Ma@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>