aspeed: Add AST2600 platform support

Add low level platform initialization for the AST2600 SoC.
The 2-stage booting with U-Boot SPL are leveraged to support
different booting mode.

However, currently the patch supports only the booting from
memory-mapped SPI flash.

Signed-off-by: Chia-Wei, Wang <chiawei_wang@aspeedtech.com>
Reviewed-by: Ryan Chen <ryan_chen@aspeedtech.com>

include/configs/evb_ast2600.h

@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright (c) Aspeed Technology Inc.
+ */
+
+#ifndef __CONFIG_H
+#define __CONFIG_H
+
+#include <configs/aspeed-common.h>
+
+#define CONFIG_SYS_UBOOT_BASE		CONFIG_SYS_TEXT_BASE
+
+/* Memory Info */
+#define CONFIG_SYS_LOAD_ADDR		0x83000000
+
+#endif	/* __CONFIG_H */