hwc/overlay: Add support for pipe priorities, 1 pipe config for FB

If using source split to stage 2 pipes on the same mixer stage,
the left pipe needs to be a higher priority than the right.

Add API in overlay to compare pipe priorities and use this in
source split config to stage pipes accordingly.

Add support for 1 pipe config for FB if updating rect is within 2048
pixels.

Change-Id: I8b33d5ebd0f8765ee842bab128d8abd67a110145
diff --git a/liboverlay/pipes/overlayGenPipe.cpp b/liboverlay/pipes/overlayGenPipe.cpp
index 9e57223..303cd34 100644
--- a/liboverlay/pipes/overlayGenPipe.cpp
+++ b/liboverlay/pipes/overlayGenPipe.cpp
@@ -106,6 +106,10 @@
     return mCtrl->getCrop();
 }
 
+uint8_t GenericPipe::getPriority() const {
+    return mCtrl->getPriority();
+}
+
 void GenericPipe::dump() const
 {
     ALOGE("== Dump Generic pipe start ==");