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 and DCN2.

In addition, future HW will need to access the HUBPREQ_DEBUG and
CUR_TTU_CNTL0 register for hubp_init. Add that here.

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