hwc: For FB target check RGB pipe availability before VG pipe

If RGB pipe is available then it should be allocated before
allocating VG pipe for FB target.

Change-Id: I0c1f0fd08a7779eb077e9e9c1809bdbcaff2227c
hwc: Disable mdp comp if mDownscaleMode is set for external

If mDownscaleMode is on then scaling will be done. Sending a RGB
layer with alpha to VG pipe can cause composition issues.

Change-Id: I215a5d7360fe741124e809be0b66c328c943d7dc
overlay: Allocate from MM heap as a fallback

 * Not all devices support IOMMU yet, so use the MM heap as a fallback.
 * Enabled when NO_IOMMU is set

Change-Id: I9d9f3dffb92f5b4bf45422df0f66a40611943202
display: Cover NO_IOMMU for msm7x30/msm7x27a too

Change-Id: Ic68672f386a06fd0ac9fd1f18eec3188415a8642
hwc: rotator is not supported on msm7x27a

Change-Id: I26fe237831eb6fa41968d5eb6a75938e6dc53183
gralloc: Allow legacy devices to use PMEM for ADSP (camera).

Partially bring back PMEM support for legacy devices having proprietary camera
libraries stuck in PMEM. This change allows these devices to continue using
PMEM for the camera, and ION for everything else.

Change-Id: I1afbc7d137b3d49b2ab3e53917b16fd920ea140b