drm/amdgpu: add sdma v6_0_0 pkt header v3

v1: add sdma v6_0_0 pkt definitions (Hawking)
v2: add gcr control field definition (Likun)
v3: correct some definitions (Likun)

Signed-off-by: Hawking Zhang <Hawking.Zhang@amd.com>
Reviewed-by: Likun Gao <Likun.Gao@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>