[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/Kconfig b/drivers/of/Kconfig
index c03072b..3354ad7 100644
--- a/drivers/of/Kconfig
+++ b/drivers/of/Kconfig
@@ -1,3 +1,9 @@
 config OF_DEVICE
 	def_bool y
 	depends on OF && (SPARC || PPC_OF)
+
+config OF_GPIO
+	def_bool y
+	depends on OF && PPC_OF && HAVE_GPIO_LIB
+	help
+	  OpenFirmware GPIO accessors