ARM: dts: am43xx: Introduce MUX_MODE9 for pinctrl

Some pins on AM43XX support MODE9 for the pinctrl settings so add a
binding to describe this.

Signed-off-by: Dave Gerlach <d-gerlach@ti.com>
Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>

include/dt-bindings/pinctrl/am43xx.h

@@ -14,6 +14,7 @@
 #define MUX_MODE6	6
 #define MUX_MODE7	7
 #define MUX_MODE8	8
+#define MUX_MODE9	9
 
 #define PULL_DISABLE		(1 << 16)
 #define PULL_UP			(1 << 17)