This implements various helpers to support OF bindings for the GPIO
LIB API.

Previously this was PowerPC specific, but it seems this code isn't
arch-dependent anyhow, so let's place it into of/.

SPARC will not see this addition yet, real hardware seem to not use
GPIOs at all. But this might change:

   http://www.leox.org/docs/faq_MLleon.html

"16-bit I/O port" sounds promising. :-)
Signed-off-by: NAnton Vorontsov <avorontsov@ru.mvista.com>
Acked-by: NGrant Likely <grant.likely@secretlab.ca>
Signed-off-by: NPaul Mackerras <paulus@samba.org>