hwc: Add deduction operation to Rect utils

Seperate out rectangle deduction from the layer cropping. Update
layer sourceCrop and displayFrame after deducting the rect value.
This makes the function generic enough to be used by other
modules

Change-Id: I587ac951357af823a1bf5e06c15ff47ac6a9c2a0
hwc: Crop source rect for the optimized destination

If a layer destination can be optimized, its source rect
needs to be cropped for the optimized destination rect.

Change-Id: If9a9891200d9cea52b58b253299b4007197cd9e5