asm-generic: fix the inclusion guards for cacheflush.h

cacheflush.h uses a somewhat to generic include guard name that clashes
with various arch files.  Use a more specific one.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Link: http://lkml.kernel.org/r/20200515143646.3857579-6-hch@lst.de


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>