mips: mtmips: add support for MediaTek MT7620 SoC

This patch adds support for MediaTek MT7620 SoC.
All files are dedicated for u-boot.

Reviewed-by: Stefan Roese <sr@denx.de>
diff --git a/arch/mips/mach-mtmips/Makefile b/arch/mips/mach-mtmips/Makefile
index a7e6a66..4909b47 100644
--- a/arch/mips/mach-mtmips/Makefile
+++ b/arch/mips/mach-mtmips/Makefile
@@ -5,4 +5,5 @@
 obj-y += ddr_cal.o
 obj-$(CONFIG_SPL_BUILD) += spl.o
 
+obj-$(CONFIG_SOC_MT7620) += mt7620/
 obj-$(CONFIG_SOC_MT7628) += mt7628/