mm/rmap: rename COMPOUND_MAPPED to ENTIRELY_MAPPED

We removed all "bool compound" and RMAP_COMPOUND parameters.  Let's remove
the remaining "compound" terminology by making COMPOUND_MAPPED match the
"folio->_entire_mapcount" terminology, renaming it to ENTIRELY_MAPPED.

ENTIRELY_MAPPED is only used when the whole folio is mapped using a single
page table entry (e.g., a single PMD mapping a PMD-sized THP).  For now,
we don't support mapping any THP bigger than that, so ENTIRELY_MAPPED only
applies to PMD-mapped PMD-sized THP only.

Link: https://lkml.kernel.org/r/20231220224504.646757-40-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Yin Fengwei <fengwei.yin@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>