mm: add generic flush_icache_pages() and documentation

flush_icache_page() is deprecated but not yet removed, so add a range
version of it.  Change the documentation to refer to
update_mmu_cache_range() instead of update_mmu_cache().

Link: https://lkml.kernel.org/r/20230802151406.3735276-4-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: Mike Rapoport (IBM) <rppt@kernel.org>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>