dts: move device tree sources to arch/$(ARCH)/dts/

Unlike Linux Kernel, U-Boot historically had *.dts files under
board/$(VENDOR)/dts/ and *.dtsi files under arch/$(ARCH)/dts/.

I think arch/$(ARCH)/dts dicretory is a better location
to store both *.dts and *.dtsi files.

For example, before this commit, board/xilinx/dts directory
had both Microblaze dts (microblaze-generic.dts) and
ARM dts (zynq-*.dts), which are totally unrelated.

This commit moves *.dts to arch/$(ARCH)/dts/ directories,
allowing us to describe nicely mutiple DTBs generation in the next commit.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>

board/toradex/dts/tegra20-colibri_t20_iris.dts

@@ -1,45 +0,0 @@
-/dts-v1/;
-
-#include "tegra20.dtsi"
-
-/ {
-	model = "Toradex Colibri T20";
-	compatible = "toradex,t20", "nvidia,tegra20";
-
-	aliases {
-		usb0 = "/usb@c5008000";
-		usb1 = "/usb@c5000000";
-		usb2 = "/usb@c5004000";
-		sdhci0 = "/sdhci@c8000600";
-	};
-
-	usb@c5000000 {
-		dr_mode = "otg";
-	};
-
-	usb@c5004000 {
-		nvidia,phy-reset-gpio = <&gpio 169 0>; /* PV1 */
-		nvidia,vbus-gpio = <&gpio 217 0>; /* PBB1 */
-	};
-
-	usb@c5008000 {
-		nvidia,vbus-gpio = <&gpio 178 1>; /* PW2 low-active */
-	};
-
-	nand-controller@70008000 {
-		nvidia,wp-gpios = <&gpio 144 0>; /* PS0 */
-		nvidia,width = <8>;
-		nvidia,timing = <15 100 25 80 25 10 15 10 100>;
-
-		nand@0 {
-			reg = <0>;
-			compatible = "nand-flash";
-		};
-	};
-
-	sdhci@c8000600 {
-		status = "okay";
-		cd-gpios = <&gpio 23 1>; /* gpio PC7 */
-		bus-width = <4>;
-	};
-};