drm: msm: sde: reserve DSC in pairs for 4DSC topologies

Reserve DSC in the sequence of primary-peer and then
primary-peer again until all required DSC are reserved.

Searching sequence will not change for single/dual DSC
reservation. For single DSC reservation it will return
right after the first primary DSC is found. For dual DSC
reservation it will return after the first primary-peer
pair is found.

The logic can also work for triple/quad or any number
of DSC reservetion and make sure that all the reserved
DSCs are in pairs except the last one if total DSC number
is odd.

Change-Id: I5b90d54822ce16ef829e7c657c1b14e7a484c65a
Signed-off-by: Thomas Dedinsky <tdedinsk@codeaurora.org>