Add a boardconfig to force HWC composition of virtual displays

When this boardconfig is defined, even when all virtual display
composition is done by GLES, the HWC will be forced to copy from the
GLES framebuffer to the output buffer. On some hardware this allows
HWC to do format conversions that would otherwise have to be done by
the consumer, with worse power and/or performance.

Bug: 8316155
Change-Id: If980ecc589f138cef063eafa757f7f748196713e