libexternal: prefix the property name with hw

System property to be shared with the applications, they need
to have same UID.
Prefix the system property with "hw." so that it can be of system
UID and be accessed by any app.

Change-Id: Ie5db1b7e614728c53e1085089194cd8a58f9ae63
CRs-fixed: 456480
hwc: Use intermediate buffers for copybit

The earlier copybit solution involved blitting directly into
the SurfaceFlinger's framebuffer target. That solution involved
unnecessary framework changes and caused issues when the
framebuffer was being written to both by GL and copybit.
Update hwc_copybit to use our own buffers for this purpose.
We also make sure we display only the region we're interested in
so that unnecessary artifacts from previous blits do not show up
on the display. This way, we can avoid clearing the intermediate
buffers every frame.

Change-Id: I713b3fc606e0768444c621af76853ece41964da1
Revert "display: Disable use of copybit temporarily"

This reverts commit a9290309985df06ab025de980486110410db2b94.
hwc: Fallback to CAMERA heap when IOMMU not available