drm/amd: Put cik structures in a common place

This patch creates a new file, cik_structs.h, and puts the cik_mqd and
cik_sdma_rlc_registers structures in that file.

The new file is placed in a common include folder under the drm/amd folder, so
it will be shared among all amd drm drivers.

Signed-off-by: Ben Goz <ben.goz@amd.com>
Signed-off-by: Oded Gabbay <oded.gabbay@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>