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>

mm: remove ARCH_IMPLEMENTS_FLUSH_DCACHE_FOLIO

Current best practice is to reuse the name of the function as a define to
indicate that the function is implemented by the architecture.

Link: https://lkml.kernel.org/r/20230802151406.3735276-6-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>

cacheflush.h: Add forward declaration for struct folio

The struct folio is not declared in cacheflush.h so we need to provide
a forward declaration as otherwise users of this header file may get
warnings.

Reported-by: Guenter Roeck <linux@roeck-us.net>
Fixes: 522a0032af00 ("Add linux/cacheflush.h")
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Add linux/cacheflush.h

Many architectures do not include asm-generic/cacheflush.h, so turn
the includes on their head and add linux/cacheflush.h which includes
asm/cacheflush.h.

Move the flush_dcache_folio() declaration from asm-generic/cacheflush.h
to linux/cacheflush.h and change linux/highmem.h to include
linux/cacheflush.h instead of asm/cacheflush.h so that all necessary
places will see flush_dcache_folio().

More functions should have their default implementations moved in the
future, but those are for follow-on patches. This fixes csky, sparc and
sparc64 which were missed in the commit which added flush_dcache_folio().

Fixes: 08b0b0059bf1 ("mm: Add flush_dcache_folio()")
Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>