etnaviv: Fix missing rnndb file in tarballs

Seems that when the rnndb files for etniviv were updated/included back
in Nov 2017, hw/texdesc_3d.xml.h was missed from Makefile.sources and
meson.build. This was all during the conversion to meson, so it apears
to have slipped through the cracks. As such, this file has been missing
from the official tarballs since inclusion in Mesa, so the git trees
and tarballs differ.

Found due to lintian errors in the Debian packages.

Fixes: f1e1c60f ("etnaviv: Update from rnndb")
Cc: mesa-stable@lists.freedesktop.org
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>
(cherry picked from commit f806cc9e)