drm/amdgpu: Remove wrapper layer of cgs irq handling

v2: add Vega12 support

1. remove struct cgs_os_ops
2. delete cgs_linux.h
3. refine the irq code for vega10, can fix set pp table
   failed issue.
4. add common smu irq process function

Acked-by: Christian König <christian.koenig@amd.com>
Acked-by: Junwei Zhang <Jerry.Zhang@amd.com>
Signed-off-by: Rex Zhu <Rex.Zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>