of: use platform_device_add

This allows platform_device_add a chance to call insert_resource on all
of the resources from OF. At a minimum this fills in proc/iomem and
presumably makes resource tracking and conflict detection work better.
However, it has the side effect of moving all OF generated platform
devices from /sys/devices to /sys/devices/platform/. It /shouldn't/
break userspace because userspace is not supposed to depend on the full
path (because userspace always does what it is supposed to, right?).

This may cause breakage if either:
1) any two nodes in a given device tree have overlapping & staggered
   regions (ie. 0x80..0xbf and 0xa0..0xdf; where one is not contained
   within the other). In this case one of the devices will fail to
   register and an exception will be needed in platform_device_add() to
   complain but not fail.
2) any device calls request_mem_region() on a region larger than
   specified in the device tree. In this case the device node may be
   wrong, or the driver is overreaching. In either case I'd like to know
   about any problems and fix them.

Please test. Despite the above, I'm still fairly confident that this
patch is in good shape. I'd like to put it into linux-next, but would
appreciate some bench testing from others before I do; particularly on
PowerPC machines.

v2: Remove powerpc special-case

Cc: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Rob Herring <rob.herring@calxeda.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>