ARM: dts: ti: omap: am335x-regor: Fix RS485 settings

RTS pin seems to have inverted behavior on am335x, other than expected
with default "rs485-rts-active-high" (instead of low on idle, high on send,
it is the opposite). Transceiver datasheet also suggests a pulldown.
Add includes to pin definitions that are used.

Signed-off-by: Steffen Hemer <s.hemer@phytec.de>
Signed-off-by: Dominik Haller <d.haller@phytec.de>
Link: https://lore.kernel.org/r/20240730092353.10209-1-d.haller@phytec.de
Signed-off-by: Kevin Hilman <khilman@baylibre.com>

arch/arm/boot/dts/ti/omap/am335x-regor.dtsi

@@ -5,6 +5,9 @@
  *
  */
 
+#include <dt-bindings/gpio/gpio.h>
+#include <dt-bindings/pinctrl/am33xx.h>
+
 / {
 	model = "Phytec AM335x phyBOARD-REGOR";
 	compatible = "phytec,am335x-regor", "phytec,am335x-phycore-som", "ti,am33xx";
@@ -188,7 +191,7 @@
 		pinctrl-single,pins = <
 			AM33XX_PADCONF(AM335X_PIN_UART1_RXD, PIN_INPUT_PULLUP, MUX_MODE0)
 			AM33XX_PADCONF(AM335X_PIN_UART1_TXD, PIN_OUTPUT_PULLDOWN, MUX_MODE0)
-			AM33XX_PADCONF(AM335X_PIN_UART1_RTSN, PIN_OUTPUT_PULLUP, MUX_MODE0)
+			AM33XX_PADCONF(AM335X_PIN_UART1_RTSN, PIN_OUTPUT_PULLDOWN, MUX_MODE0)
 		>;
 	};
 };
@@ -198,4 +201,9 @@
 	pinctrl-0 = <&uart1_rs485_pins>;
 	status = "okay";
 	linux,rs485-enabled-at-boot-time;
+	/*
+	 * un-intuitively, yet with the default (active-high),
+	 * am335x RTS is high on idle and gets low on active !
+	 */
+	rs485-rts-active-low;
 };