hwc: Add support for configuring maximum mdp layers on secondary

Add support for configuring the maximum mdp layers on secondary
via persist.hwc.maxseclayers property. The default value is 1.

Move the check for max allowed layers to postHeuristicsHandling
rather than it being a part of strategies itself.

Change-Id: Icae6cb7e400fd95f60e0b3eb64e6b768e4dbd861
2 files changed