etnaviv: nir: add etna_nir_lower_to_source_mods(..)

This is more or less a copy of nir_lower_to_source_mods(..) with
the following differences:

 - we store the source mods in pass_flags
 - we do not try to saturate the destination

Signed-off-by: Christian Gmeiner <cgmeiner@igalia.com>
Acked-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Acked-by: Yonggang Luo <luoyonggang@gmail.com>
Acked-by: Lucas Stach <l.stach@pengutronix.de>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24216>
3 files changed