i915: convert shmem_sg_free_table() to use a folio_batch

Remove a few hidden compound_head() calls by converting the returned page
to a folio once and using the folio APIs.  We also only increment the
refcount on the folio once instead of once for each page.  Ideally, we
would have a for_each_sgt_folio macro, but until then this will do.

Link: https://lkml.kernel.org/r/20230621164557.3510324-5-willy@infradead.org


Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>