m32r: add definition of ioremap_wc to io.h

Before adding a resource managed ioremap_wc function, we need
to have ioremap_wc defined for m32r to prevent build errors.

Signed-off-by: Abhilash Kesavan <a.kesavan@samsung.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>