anv: do not advertise AHW support if extension not enabled

anv: do not advertise AHW support if extension not enabled

Fixes following failing vk-gl-cts cases on Linux desktop:

   dEQP-VK.api.external.memory.android_hardware_buffer.suballocated.buffer.info
   dEQP-VK.api.external.memory.android_hardware_buffer.suballocated.image.info
   dEQP-VK.api.external.memory.android_hardware_buffer.dedicated.image.info
   dEQP-VK.api.external.memory.android_hardware_buffer.dedicated.buffer.info

Fixes: 517103abf1c "anv/android: add ahardwarebuffer external memory properties"
Reported-by: Juan A. Suarez <jasuarez@igalia.com>
Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Juan A. Suarez <jasuarez@igalia.com>