Revert "nir: replace lower_ffma and fuse_ffma with has_ffma"

This reverts commit 939ddf3f67de2ed1700c093e60cf95c1b72ff20b.

Intel has a separate pass for fusing FFMAs selectively.  We split
these flags in commit 1b72c31e1f1947123d8c236b56e230f030f60cf9 and
the reasoning still stands.  The patch being reverted was just a
cleanup, so there should be no issue with reverting it.

Acked-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6849>
19 files changed