hwc: Add target specific checks in hwcomposer

* Mdss driver supports DMA-Multiplexing on wb interface
for certain targets. Add overlay get function to query
this info during pipe allocation for wb.

* UI Scaling on external is not supported on certain
targets due to the lack of availability of pipes with
scalars. Add overlay get function to query this info
to disable action-safe calcs, DRC and others which
require downscaling.

Change-Id: I1726caa4634f72d781561e797078648524ea2eef
diff --git a/libhwcomposer/hwc_fbupdate.cpp b/libhwcomposer/hwc_fbupdate.cpp
index 74e6da4..0374dec 100644
--- a/libhwcomposer/hwc_fbupdate.cpp
+++ b/libhwcomposer/hwc_fbupdate.cpp
@@ -192,7 +192,7 @@
                   (mDpy && !extOrient
                   && !ctx->dpyAttr[mDpy].mDownScaleMode))
                   && (extOnlyLayerIndex == -1)) {
-            if(!qdutils::MDPVersion::getInstance().is8x26() &&
+            if(ctx->mOverlay->isUIScalingOnExternalSupported() &&
                 !ctx->dpyAttr[mDpy].customFBSize) {
                 getNonWormholeRegion(list, sourceCrop);
                 displayFrame = sourceCrop;