iris: Drop copy format hacks from copy region based transfer path.

This doesn't work for compressed formats, as the source texture and
temporary texture would have different block sizes.  (Forcing the driver
to always take the GPU path would expose the bug.)  Instead, just use
the source format for the temporary, and let blorp_copy deal with
overrides.

The one case where we can't do this is ASTC, because isl won't let us
create a linear ASTC surface.  Fall back to the CPU paths there for now.

Fixes: 9d1334d2 ("iris: Use copy_region and staging resources to avoid transfer stalls")
Reviewed-by: Rafael Antognolli <rafael.antognolli@intel.com>
(cherry picked from commit 136629a1)