etnaviv: sync uapi header

Import the etnaviv header changes from kernel commits 9ad59fea162c
("drm/etnaviv: submit support for in-fences") and 78ec187f64fa
("drm/etnaviv: submit support for out-fences") for fence fd support.

The drm_etnaviv_gem_submit structure was extended to include a flags
field, new flags for in-fence and out-fence fds and an input/output
fence fd field.

This is one-way backwards compatible because old userspace code passing
a short structure not including the flags field to new kernels will
cause the remaining fields to be zero-filled. New userspace code must
make sure to only pass the short structure to old kernels, though.

Not generated using make headers_install, since the drm/etnaviv_drm.h
uapi header is not installed yet by the kernel.
Copied from the airlied/drm-next commit 78ec187f64fa.

v2: improved commit message

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>