mips: mtmips: add support for MediaTek MT7621 SoC

This patch adds support for MediaTek MT7621 SoC.
All files are dedicated for u-boot.

The default build target is u-boot-mt7621.bin.

The specification of this chip:
https://www.mediatek.com/products/homenetworking/mt7621

Reviewed-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Signed-off-by: Weijie Gao <weijie.gao@mediatek.com>

include/configs/mt7621.h

@@ -0,0 +1,43 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2022 MediaTek Inc. All rights reserved.
+ *
+ * Author: Weijie Gao <weijie.gao@mediatek.com>
+ */
+
+#ifndef __CONFIG_MT7621_H
+#define __CONFIG_MT7621_H
+
+#define CONFIG_SYS_MIPS_TIMER_FREQ	440000000
+
+#define CONFIG_SYS_SDRAM_BASE		0x80000000
+
+#define CONFIG_VERY_BIG_RAM
+#define CONFIG_MAX_MEM_MAPPED		0x1c000000
+
+#define CONFIG_SYS_INIT_SP_OFFSET	0x800000
+
+#define CONFIG_SYS_NONCACHED_MEMORY	0x100000
+
+/* MMC */
+#define MMC_SUPPORTS_TUNING
+
+/* NAND */
+#define CONFIG_SYS_MAX_NAND_DEVICE	1
+
+/* Serial SPL */
+#if defined(CONFIG_SPL_BUILD) && defined(CONFIG_SPL_SERIAL)
+#define CONFIG_SYS_NS16550_MEM32
+#define CONFIG_SYS_NS16550_CLK		50000000
+#define CONFIG_SYS_NS16550_REG_SIZE	-4
+#define CONFIG_SYS_NS16550_COM1		0xbe000c00
+#endif
+
+/* Serial common */
+#define CONFIG_SYS_BAUDRATE_TABLE	{ 9600, 19200, 38400, 57600, 115200, \
+					  230400, 460800, 921600 }
+
+/* Dummy value */
+#define CONFIG_SYS_UBOOT_BASE		0
+
+#endif /* __CONFIG_MT7621_H */