Wrapper to android native window api located in aosp system/window.h.
Allow to queue/dequeue hw buffers (ANativeWindowBuffer_t) allocated with a
speficied hal_format and hw_usage.

This requires changes to the android build project to include
iomx_hwbuffer.c when building libiomx-*.so.
Signed-off-by: Martin Storsjö <martin@martin.st>