drm/amd/display: Add hubp_init entry to hubp vtable

drm/amd/display: Add hubp_init entry to hubp vtable

Different HW will need to init HUBP differently. For now, add a vtable
entry, and hook a NO-OP for DCN1.

In addition, future HW will need to access the HUBPREQ_DEBUG register
for hubp_init. Add it to the reg list.

Signed-off-by: Charlene Liu <charlene.liu@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>