drm/amdgpu: Refine CSA related functions

There is no functional changes,
Use function arguments for SRIOV special variables which
is hardcode in those functions.

so we can share those functions in baremetal.

Reviewed-by: Monk Liu <Monk.Liu@amd.com>
Signed-off-by: Rex Zhu <Rex.Zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>