The VK_ANDROID_native_buffer extension is missing from the official
vk.xml. This patch defines the extension in a separate, minimal XML
file: vk_android_native_buffer.xml.

I chose to add the extension to a new XML file instead of adding it to
the official vk.xml in order to avoid conflicts each time we sync the
vk.xml from Khronos.

This should be only a temporary solution until Jesse Hall is persuaded
to add it to the official vk.xml.

Reviewed-by: Tapani Pälli <tapani.palli@intel.com>