hwc: Add support for secure RGB layer

1. Detect and account the number of secure RGB layers present.
2. Mark secure RGB layers for MDP comp in cache based stratergy.
3. If full MDP comp and partial MDP comp fails, Mark secure RGB
   layers for MDP composition.
4. In partial MDP comp reject load based composition, if secure
   layer is present to avoid GPU composition.
5. Disable idlefallback feature if secure RGB layer is present
   to avoid GPU composition.

Change-Id: Idb4c4f09b081ec20240a2602aa3f20332fa49ad6