nommu: add ioremap_page_range()

lib/ioremap.c is presently only built in if CONFIG_MMU is set.  While this
is reasonable, platforms that support both CONFIG_MMU=y or n need to be
able to call in to this regardless.

As none of the current nommu platforms do anything special with ioremap(),
we assume that it's always successful.

This fixes the SH-4 build with CONFIG_MMU=n.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>