[MTD][NOR] Add physical address to point() method

Adding the ability to get a physical address from point() in addition
to virtual address.  This physical address is required for XIP of
userspace code from flash.

Signed-off-by: Jared Hulbert <jaredeh@gmail.com>
Reviewed-by: Jörn Engel <joern@logfs.org>
Acked-by: Nicolas Pitre <nico@cam.org>
Acked-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>