i965: Accept CONTEXT_ATTRIB_PRIORITY for brwCreateContext

i965: Accept CONTEXT_ATTRIB_PRIORITY for brwCreateContext

The forward port of commit 6d87500fe12e ("dri: Change
__DriverApiRec::CreateContext to take a struct for attribs") failed to
adapt the set of allowed attributes for the earlier introduction of
context priorities (commit 1617fca6d12e "i965: Pass the EGL/DRI context
priority through to the kernel").

Fixes: 6d87500fe12e ("dri: Change __DriverApiRec::CreateContext to take a struct for attribs")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Adam Jackson <ajax@redhat.com>
Cc: Nicolai Hähnle <nicolai.haehnle@amd.com>
Cc: Emil Velikov <emil.velikov@collabora.com>
Cc: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
Cc: mesa-stable@lists.freedesktop.org