of/device: merge of_device_uevent

Merge common code between powerpc and microblaze

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
CC: Michal Simek <monstr@monstr.eu>
CC: Wolfram Sang <w.sang@pengutronix.de>
CC: Stephen Rothwell <sfr@canb.auug.org.au>
CC: Benjamin Herrenschmidt <benh@kernel.crashing.org>
CC: microblaze-uclinux@itee.uq.edu.au
CC: linuxppc-dev@ozlabs.org