powerpc: unexport flush_icache_user_range

flush_icache_user_range is only used by copy_to_user_page, which is only
used by core VM code.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Link: http://lkml.kernel.org/r/20200515143646.3857579-4-hch@lst.de


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