gallium: introduce PIPE_CAP_MEMOBJ

This can be used to guard support for EXT_memory_object and related
extensions.

v2: update gallium docs

v3 (Timothy Arceri):
 - add cap to nv50

Signed-off-by: Andres Rodriguez <andresx7@gmail.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
17 files changed