drm/amd: Add CGS interfaces

CGS (Common Graphics Services) is an AMD cross component
abstraction layer to designed to better encapsulate
specific IP block drivers so different teams can effectively
work on differnet IP block drivers independently. It provides
a common interface for things like accessing registers,
allocating GPU memory, and registering interrupt sources.
The plan is to eventually move more and more IP drivers to
this interface.  The first user is the ACP IP driver.

Reviewed-by: Jammy Zhou <Jammy.Zhou@amd.com>
Signed-off-by: Chunming Zhou <David1.Zhou@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>