[POWERPC] OF helpers for the GPIO API

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: Anton Vorontsov <avorontsov@ru.mvista.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/drivers/of/Makefile b/drivers/of/Makefile
index ab9be5d..5a61f70 100644
--- a/drivers/of/Makefile
+++ b/drivers/of/Makefile
@@ -1,2 +1,3 @@
 obj-y = base.o
 obj-$(CONFIG_OF_DEVICE) += device.o platform.o
+obj-$(CONFIG_OF_GPIO)   += gpio.o