gallium: add external usage flags to resource_from(get)_handle (v2)

This will allow drivers to make better decisions about texture sharing
for DRI2, DRI3, Wayland, and OpenCL.

v2: add read/write flags, take advantage of __DRI_IMAGE_USE_BACKBUFFER

Reviewed-by: Axel Davy <axel.davy@ens.fr>
30 files changed