mesa: add support for memory object creation/import/delete

mesa: add support for memory object creation/import/delete

Used by EXT_external_objects and EXT_external_objects_fd

V2 (Timothy Arceri):
 - Throw GL_OUT_OF_MEMORY error if CreateMemoryObjectsEXT()
   fails.
 - C99 tidy ups
 - remove void cast (Constantine Kharlamov)

V3 (Timothy Arceri):
 - rename mo -> memObj
 - check that the object is not NULL before initializing
 - add missing "EXT" in function error message

V4 (Timothy Arceri):
 - remove checks for (memory objecy id == 0) and catch in
   _mesa_lookup_memory_object() instead.

Signed-off-by: Andres Rodriguez <andresx7@gmail.com>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>