Add of_driver_match_device() helper function.  This function can be used
by bus types to determine if a driver works with a device when using OF
style matching.  If CONFIG_OF is unselected, then it is a nop.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
CC: Greg Kroah-Hartman <gregkh@suse.de>
CC: Michal Simek <monstr@monstr.eu>
CC: Grant Likely <grant.likely@secretlab.ca>
CC: Benjamin Herrenschmidt <benh@kernel.crashing.org>
CC: Stephen Rothwell <sfr@canb.auug.org.au>
CC: linux-kernel@vger.kernel.org
CC: microblaze-uclinux@itee.uq.edu.au
CC: linuxppc-dev@ozlabs.org
CC: devicetree-discuss@lists.ozlabs.org