airoha: Add initial support for Airoha AN7581 SoC

Add initial support for Airoha AN7581 SoC. This adds the initial Kconfig
and Makefile entry for the SoC, an U-Boot specific DTSI and initial config
for it. Also add the initial code for CPU and RAM initialization.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>

include/configs/an7581.h

@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Configuration for Airoha AN7581
+ */
+
+#ifndef __AN7581_H
+#define __AN7581_H
+
+#include <linux/sizes.h>
+
+#define CFG_SYS_UBOOT_BASE		CONFIG_TEXT_BASE
+
+#define CFG_SYS_INIT_RAM_ADDR           CONFIG_TEXT_BASE
+#define CFG_SYS_INIT_RAM_SIZE           SZ_2M
+
+/* DRAM */
+#define CFG_SYS_SDRAM_BASE		0x80000000
+
+#endif