pinctrl: at91: add slewrate support for SAM9X60

Add slew rate support for SAM9X60 pin controller.

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Acked-by: Ludovic Desroches <ludovic.desroches@microchip.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

include/dt-bindings/pinctrl/at91.h

@@ -17,6 +17,7 @@
 #define AT91_PINCTRL_DIS_SCHMIT		(1 << 4)
 #define AT91_PINCTRL_OUTPUT		(1 << 7)
 #define AT91_PINCTRL_OUTPUT_VAL(x)	((x & 0x1) << 8)
+#define AT91_PINCTRL_SLEWRATE		(1 << 9)
 #define AT91_PINCTRL_DEBOUNCE		(1 << 16)
 #define AT91_PINCTRL_DEBOUNCE_VAL(x)	(x << 17)
 
@@ -27,6 +28,9 @@
 #define AT91_PINCTRL_DRIVE_STRENGTH_MED			(0x2 << 5)
 #define AT91_PINCTRL_DRIVE_STRENGTH_HI			(0x3 << 5)
 
+#define AT91_PINCTRL_SLEWRATE_DIS	(0x0 << 9)
+#define AT91_PINCTRL_SLEWRATE_ENA	(0x1 << 9)
+
 #define AT91_PIOA	0
 #define AT91_PIOB	1
 #define AT91_PIOC	2