pinctrl: at91-pio4: Add pinctrl driver

AT91 PIO4 controller is a combined gpio-controller, pin-mux and
pin-config module. The peripheral's pins are assigned through
per-pin based muxing logic.

The pin configuration is performed on specific registers which
are shared along with the gpio controller. So regard the pinctrl
device as a child of atmel_pio4 device.

Signed-off-by: Wenyou Yang <wenyou.yang@atmel.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Andreas Bießmann <andreas@biessmann.org>
diff --git a/drivers/pinctrl/Kconfig b/drivers/pinctrl/Kconfig
index 2972dba..44b53b9 100644
--- a/drivers/pinctrl/Kconfig
+++ b/drivers/pinctrl/Kconfig
@@ -141,6 +141,13 @@
 	  definitions and pin control functions for each available multiplex
 	  function.
 
+config PINCTRL_AT91PIO4
+	bool "AT91 PIO4 pinctrl driver"
+	depends on DM
+	help
+	  This option is to enable the AT91 pinctrl driver for AT91 PIO4
+	  controller which is available on SAMA5D2 SoC.
+
 config PINCTRL_SANDBOX
 	bool "Sandbox pinctrl driver"
 	depends on SANDBOX