hwc: In MDPcomp, set isFg flag for the first layer

Set isFg flag for the layer with zorder 0 for proper blending
to happen in Mdp composition.

Change-Id: Ibcb158f2049aa8713267feec93f299866fe74d52
CRs-Fixed: 481497
liboverlay : unset basepipe on overlay intialization.

On display framework intialization or restart when we are unsetting
stale MDP pipes connected to mixer, free base pipe too. Base pipe
gets allocated before composition once on start or restart of framework.

Change-Id: Ie73915031ffbcf03b6cadf2c526c76be79d582be
CRs-fixed: 483142
hwc/copybit: Add check for Max layers support.

Add check in copybit for Max. layers supported by HWC. Increase
max. RGB surfaces to MAX_NUM_LAYERS to support known use cases.

CRs-Fixed: 481226
Change-Id: Ie30ab0ef3047a304133cb547902ae11fecc5db22