Add a function which reads resources from a device, such as the device
hardware address. This uses the "reg" property in the device.

Unlike other functions there is little sense in inlining this when
livetree is not being used because it has some logic in it and this would
just bloat the code size.
Signed-off-by: NSimon Glass <sjg@chromium.org>
Tested-by: NMarcel Ziswiler <marcel.ziswiler@toradex.com>
Tested-on: Beaver, Jetson-TK1