ARM: dts: i.MX6UL: U-Boot specific dts for u-boot, dm-spl

u-boot,dm-spl property is specific to U-Boot, so move it into
*u-boot.dtsi files for relevant i.MX6UL files.

This make syncing Linux dts files straight forward.

Also update the MAINTAINERS file for dts files.

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
diff --git a/arch/arm/dts/imx6ul-geam-kit-u-boot.dtsi b/arch/arm/dts/imx6ul-geam-kit-u-boot.dtsi
new file mode 100644
index 0000000..d1b77ba
--- /dev/null
+++ b/arch/arm/dts/imx6ul-geam-kit-u-boot.dtsi
@@ -0,0 +1,25 @@
+/*
+ * Copyright (C) 2018 Jagan Teki <jagan@amarulasolutions.com>
+ *
+ * SPDX-License-Identifier:     GPL-2.0+
+ */
+
+#include "imx6ul-u-boot.dtsi"
+
+&usdhc1 {
+	u-boot,dm-spl;
+};
+
+&iomuxc {
+	pinctrl_usdhc1: usdhc1grp {
+		u-boot,dm-spl;
+	};
+
+	pinctrl_usdhc1_100mhz: usdhc1grp100mhz {
+		u-boot,dm-spl;
+	};
+
+	pinctrl_usdhc1_200mhz: usdhc1grp200mhz {
+		u-boot,dm-spl;
+	};
+};