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>
diff --git a/arch/mips/mach-mtmips/mt7621/Makefile b/arch/mips/mach-mtmips/mt7621/Makefile
new file mode 100644
index 0000000..bf1b0bb
--- /dev/null
+++ b/arch/mips/mach-mtmips/mt7621/Makefile
@@ -0,0 +1,14 @@
+# SPDX-License-Identifier: GPL-2.0
+
+obj-y += init.o
+obj-y += serial.o
+
+ifeq ($(CONFIG_SPL_BUILD),y)
+ifeq ($(CONFIG_TPL_BUILD),y)
+obj-y += tpl/
+else
+obj-y += spl/
+endif
+
+obj-y += sram_init.o
+endif