arm: mediatek: add support for MediaTek MT7988 SoC

This patch adds basic support for MediaTek MT7988 SoC.
This includes files that will initialize the SoC after boot and
its device tree.

diff --git a/arch/arm/mach-mediatek/mt7988/init.c b/arch/arm/mach-mediatek/mt7988/init.c
new file mode 100644
index 0000000..082f12b
--- /dev/null
+++ b/arch/arm/mach-mediatek/mt7988/init.c
@@ -0,0 +1,63 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2022 MediaTek Inc.
+ * Author: Sam Shih <sam.shih@mediatek.com>
+ */
+
+#include <fdtdec.h>
+#include <init.h>
+#include <asm/armv8/mmu.h>
+#include <asm/global_data.h>
+#include <asm/u-boot.h>
+#include <asm/system.h>
+
+DECLARE_GLOBAL_DATA_PTR;
+
+#define SZ_8G				_AC(0x200000000, ULL)
+
+int dram_init(void)
+{
+	int ret;
+
+	ret = fdtdec_setup_mem_size_base();
+	if (ret)
+		return ret;
+
+	gd->ram_size = get_ram_size((void *)gd->ram_base, SZ_8G);
+
+	return 0;
+}
+
+int dram_init_banksize(void)
+{
+	gd->bd->bi_dram[0].start = gd->ram_base;
+	gd->bd->bi_dram[0].size = gd->ram_size;
+
+	return 0;
+}
+
+void reset_cpu(ulong addr)
+{
+	psci_system_reset();
+}
+
+static struct mm_region mt7988_mem_map[] = {
+	{
+		/* DDR */
+		.virt = 0x40000000UL,
+		.phys = 0x40000000UL,
+		.size = 0x200000000ULL,
+		.attrs = PTE_BLOCK_MEMTYPE(MT_NORMAL) | PTE_BLOCK_OUTER_SHARE,
+	}, {
+		.virt = 0x00000000UL,
+		.phys = 0x00000000UL,
+		.size = 0x40000000UL,
+		.attrs = PTE_BLOCK_MEMTYPE(MT_DEVICE_NGNRNE) |
+			 PTE_BLOCK_NON_SHARE |
+			 PTE_BLOCK_PXN | PTE_BLOCK_UXN
+	}, {
+		0,
+	}
+};
+
+struct mm_region *mem_map = mt7988_mem_map;