drm/amdgpu: Move common code to amdgpu_gfx.c

move common code to amdgpu_gfx_enable_kcq,so
this function can be shared with gfx8 and gfx9

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