vc-sm-cma: Restore correct cache maintainance operations

We have been using the more expensive flush operations rather than
invalidate and clean since kernel rpi-5.9.y

These are exposed with:
52f14535 Re-expose some dmi APIs for use in VCSM

But I believe that commit was dropped when (non-cma) vc-sm was dropped,
and didn't get updated when the commit was restored

Signed-off-by: Dom Cobley <popcornmix@gmail.com>