drm/amdgpu: Set snoop bit for SDMA for MI series

drm/amdgpu: Set snoop bit for SDMA for MI series

SDMA writes has to probe invalidate RW lines. Set snoop bit in mmhub for
this to happen.

v2: Missed a few mmhub_v9_4. Added now.
v3: Calculate hub offset once since it doesn't change inside the loop
    Modified function names based on review comments.

Signed-off-by: Harish Kasiviswanathan <Harish.Kasiviswanathan@amd.com>
Reviewed-by: Philip Yang <Philip.Yang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>