imxrt1020: migrate to build system included -u-boot.dtsi

Migrate to using automatic build system included -u-boot.dtsi device
tree include files.

Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Reviewed-by: Giulio Benetti <giulio.benetti@benettiengineering.com>
Tested-by: Giulio Benetti <giulio.benetti@benettiengineering.com>
diff --git a/arch/arm/dts/imxrt1020-evk-u-boot.dtsi b/arch/arm/dts/imxrt1020-evk-u-boot.dtsi
index 9e1b074..7cab486 100644
--- a/arch/arm/dts/imxrt1020-evk-u-boot.dtsi
+++ b/arch/arm/dts/imxrt1020-evk-u-boot.dtsi
@@ -67,9 +67,6 @@
 
 	imxrt1020-evk {
 		u-boot,dm-spl;
-		pinctrl_lpuart1: lpuart1grp {
-			u-boot,dm-spl;
-		};
 
 		pinctrl_semc: semcgrp {
 			u-boot,dm-spl;
@@ -81,6 +78,10 @@
 	};
 };
 
+&pinctrl_lpuart1 {
+	u-boot,dm-spl;
+};
+
 &usdhc1 {
 	u-boot,dm-spl;
 };