omxil: Allow using IOMX on Android

omxil: Allow using IOMX on Android

This adds a fake OMX core implementation, relying the calls
via IOMX to the media server, which contains the actual
OMX core.

Building with IOMX requires private Android headers from the
Android source tree, namely the frameworks/base and
system/core repositories. (Either froyo or gingerbread
should work for building.) This API is not public, has no
ABI guarantees and isn't supported.

Linking also requires libraries extracted from a
froyo/gingerbread device or emulator.

Since there are no ABI guarantees, linking to this API might
make the .so fail to load on some devices, so for proper use
it should be in a dynamically loaded module, separate from the
rest of the VLC core and modules.

Since this can lead to crashes on unsupported devices, it should
only be used in production on whitelisted device/firmware
combinations that are known to work.

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>