sf: add support to change the size of FrameBuffer target

Add support to change the framebuffer size when there is a
notification regarding the change in size of app buffers.
This would enable to compose and display a smaller framebuffer
to Hardware Composer. The feature can be enabled using a
read-only SF property "ro.sf.enable_fb_scaling = 1" and is
restricted only for Primary displays.

Change-Id: I0ce98febcaff154f1edd791550a68486e68af8ba
CRs-Fixed: 2526524