hugetlb rmap handling differs quite a lot from "ordinary" rmap code.  For
example, hugetlb currently only supports entire mappings, and treats any
mapping as mapped using a single "logical PTE".  Let's move it out of the
way so we can overhaul our "ordinary" rmap.  implementation/interface.

Let's introduce and use hugetlb_remove_rmap() and remove the hugetlb code
from page_remove_rmap().  This effectively removes one check on the
small-folio path as well.

Add sanity checks that we end up with the right folios in the right
functions.

Note: all possible candidates that need care are page_remove_rmap() that
      pass compound=true.

Link: https://lkml.kernel.org/r/20231220224504.646757-3-david@redhat.comSigned-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Yin Fengwei <fengwei.yin@intel.com>
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>