st/nine: Drop USER_INDEX_BUFFERS check

st/nine: Drop USER_INDEX_BUFFERS check

This fixes 4a883966c1f74f43afc145d2c3d27af7b8c5e01a where the
PIPE_CAP was removed.

Now USER_INDEX_BUFFERS are always enabled remove the check and only
check for cmst_active directly.

v2: Axel pointed out the code was still needed when cmst was inactive,
    Rebase on master too
v3: Drop struct member user_ibufs also && fixup shortlog (Edward).
v4: Fix negation
v5: Use the right variable name csmt != cmst

Fixes: 4a883966c1f7 ("gallium: remove PIPE_CAP_USER_INDEX_BUFFERS")
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=99953
Reported-and-tested-by: Vinson Lee <vlee@freedesktop.org> (v1)
Cc: Marek Olšák <marek.olsak@amd.com>
Cc: Axel Davy <axel.davy@ens.fr>
Signed-off-by: Edward O'Callaghan <funfunctor@folklore1984.net>
Signed-off-by: Mike Lothian <mike@fireburn.co.uk>
Reviewed-by: Edward O'Callaghan <funfunctor@folklore1984.net>