drm/amdgpu: add sdma v4_4_2 support (v4)

Add support for SDMA 4.4.2.

v1: Create sdma_v4_4_2.[c|h] for initial support (Le)
v2: update amdgpu_ring_init call with atomic score (Hawking)
v3: Squash in sdma_start fixes (Alex)
v4: Comment out currently unused RAS code (Alex)

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