pinctrl: am43xx: dt-bindings: add MUX_MODE8

AM43xx devices have an extra MUX_MODE for certain pins.
Updating dt include to have MUX_MODE8 which maps to 0x8.

Signed-off-by: Darren Etheridge <detheridge@ti.com>
Signed-off-by: Sourav Poddar <sourav.poddar@ti.com>
Signed-off-by: Benoit Cousson <bcousson@baylibre.com>

include/dt-bindings/pinctrl/am43xx.h

@@ -13,6 +13,7 @@
 #define MUX_MODE5	5
 #define MUX_MODE6	6
 #define MUX_MODE7	7
+#define MUX_MODE8	8
 
 #define PULL_DISABLE		(1 << 16)
 #define PULL_UP			(1 << 17)