pinctrl: support pinconfig on the U300

This adds pin configuration support for the U300 driver pair,
we can now read out the biasing and drive mode in debugfs and
configure it using the new configuration API.

ChangeLog v1->v2:
- Migrate to pin config and generic pin config changes.
ChangeLog v2->v3:
- Adjust to generic pin config changes in v7 patch set.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
diff --git a/drivers/pinctrl/Kconfig b/drivers/pinctrl/Kconfig
index 07f3d8d..abfb964 100644
--- a/drivers/pinctrl/Kconfig
+++ b/drivers/pinctrl/Kconfig
@@ -73,6 +73,7 @@
 	bool "U300 pin controller driver"
 	depends on ARCH_U300
 	select PINMUX
+	select GENERIC_PINCONF
 
 config PINCTRL_COH901
 	bool "ST-Ericsson U300 COH 901 335/571 GPIO"