mips: Add basic MediaTek MT7620/88 support

This patch adds basic support for the MediaTek MT7620/88 SoCs. Parts of
the code is copied from the MediaTek GitHub repository:

https://github.com/MediaTek-Labs/linkit-smart-uboot.git

The mt7628a.dtsi file is imported from Linux v4.17.

Support for the LinkIt Smart 7688 module and the Gardena Smart Gateway
both based on the MT7688 will be added in further patches.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
9 files changed