anv,hasvk: android ahb is not always exportable

anv,hasvk: android ahb is not always exportable

anv_ahb_format_for_vk_format needs to know the format at least.  There
is no guarantee that AHardwareBuffer_allocate will succeed, but we are
reluctant to check with AHardwareBuffer_isSupported which may
test-allocate internally and is expensive.

v2: add anv_ahb_format_for_vk_format to anv_android_stubs.c

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22619>