drm/i915/adl_p: Add ddb allocation support

On adlp the two mbuses have two display pipes and
two DBUFS, Pipe A and D on Mbus1 and Pipe B and C on
Mbus2. The Mbus can be joined and all the DBUFS can be
used on Pipe A or B.

Bspec: 49255
Cc: Anusha Srivatsa <anusha.srivatsa@intel.com>
Signed-off-by: Vandita Kulkarni <vandita.kulkarni@intel.com>
Signed-off-by: Clinton Taylor <Clinton.A.Taylor@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210519000625.3184321-8-lucas.demarchi@intel.com