configs: am68_sk: Move to separate defconfig for AM68 SK board

Add defconfig for AM68 SK R5 and A72 configuration.

This includes and modifies the AM68 EVM defconfigs:
j721s2_evm_r5_defconfig -> am68_sk_r5_defconfig
j721s2_evm_a72_defconfig -> am68_sk_a72_defconfig

Reviewed-by: Neha Malcom Francis <n-francis@ti.com>
Signed-off-by: Manorit Chawdhry <m-chawdhry@ti.com>
diff --git a/arch/arm/dts/k3-am68-sk-base-board-u-boot.dtsi b/arch/arm/dts/k3-am68-sk-base-board-u-boot.dtsi
index b8fc62f..dca5884 100644
--- a/arch/arm/dts/k3-am68-sk-base-board-u-boot.dtsi
+++ b/arch/arm/dts/k3-am68-sk-base-board-u-boot.dtsi
@@ -129,3 +129,26 @@
 	dr_mode = "peripheral";
 	bootph-all;
 };
+
+#ifdef CONFIG_TARGET_J721S2_A72_EVM
+
+#define SPL_AM68_SK_DTB "spl/dts/k3-am68-sk-base-board.dtb"
+#define AM68_SK_DTB "u-boot.dtb"
+
+&spl_j721s2_evm_dtb {
+	filename = SPL_AM68_SK_DTB;
+};
+
+&j721s2_evm_dtb {
+	filename = AM68_SK_DTB;
+};
+
+&spl_j721s2_evm_dtb_unsigned {
+	filename = SPL_AM68_SK_DTB;
+};
+
+&j721s2_evm_dtb_unsigned {
+	filename = AM68_SK_DTB;
+};
+
+#endif