mm: rationalise flush_icache_pages() and flush_icache_page()

Move the default (no-op) implementation of flush_icache_pages() to
<linux/cacheflush.h> from <asm-generic/cacheflush.h>.  Remove the
flush_icache_page() wrapper from each architecture into
<linux/cacheflush.h>.

Link: https://lkml.kernel.org/r/20230802151406.3735276-32-willy@infradead.org


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