arm: mediatek: add support for MediaTek MT7981 SoC

This patch adds basic support for MediaTek MT7981 SoC.
This include the file that will initialize the SoC after boot and its
device tree.

Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arm/mach-mediatek/mt7981/init.c b/arch/arm/mach-mediatek/mt7981/init.c
new file mode 100644
index 0000000..4f77a3d
--- /dev/null
+++ b/arch/arm/mach-mediatek/mt7981/init.c
@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2022 MediaTek Inc.
+ * Author: Sam Shih <sam.shih@mediatek.com>
+ */
+
+#include <init.h>
+#include <asm/armv8/mmu.h>
+#include <asm/system.h>
+#include <asm/global_data.h>
+
+DECLARE_GLOBAL_DATA_PTR;
+
+int dram_init(void)
+{
+	gd->ram_size = get_ram_size((void *)CONFIG_SYS_SDRAM_BASE, SZ_2G);
+
+	return 0;
+}
+
+void reset_cpu(ulong addr)
+{
+	psci_system_reset();
+}
+
+static struct mm_region mt7981_mem_map[] = {
+	{
+		/* DDR */
+		.virt = 0x40000000UL,
+		.phys = 0x40000000UL,
+		.size = 0x80000000UL,
+		.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 = mt7981_mem_map;