imx: imx8mm/n/p-venice: enable pinctrl_wdog in SPL

Mark pinctrl_wdog as u-boot,dm-spl to clean up board code,

The set_wdog_reset() function is not necessary as this is handled by
the imx_watchdog.c driver due to the 'fsl,ext-reset-output' property
being set.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
diff --git a/arch/arm/dts/imx8mp-venice-u-boot.dtsi b/arch/arm/dts/imx8mp-venice-u-boot.dtsi
index 37f3edc..96b9fa8 100644
--- a/arch/arm/dts/imx8mp-venice-u-boot.dtsi
+++ b/arch/arm/dts/imx8mp-venice-u-boot.dtsi
@@ -72,3 +72,7 @@
 &wdog1 {
 	u-boot,dm-spl;
 };
+
+&pinctrl_wdog {
+	u-boot,dm-spl;
+};