mm: make generic_access_phys available for modules

commit 5a73633ef01cd8772defa6a3c34a588376a1df4c upstream.

In the next commit this function will be used in the uio subsystem

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>