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