iomx: add iomx_hwbuffer

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.
iomx: add android GraphicBuffers functions.

- OMXAndroid_EnableGraphicBuffers: activate GraphicBuffers.
  Next call of OMX_GetParameter(OMX_IndexParamPortDefinition) will return a
  private eColorFormat compatible with android hal_format.

- OMXAndroid_GetGraphicBufferUsage: return hw_usage that will be used to
  allocate android hw buffers.
omxil: add android hw buffers support (zero copy)

Activated if cfg "omxil-dr" is true. If extra android symbols are not found or
if HwBuffer_init() fails: fall back to non direct buffer mode