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>
diff --git a/arch/mips/mach-mt7620/Kconfig b/arch/mips/mach-mt7620/Kconfig
new file mode 100644
index 0000000..396fbd0
--- /dev/null
+++ b/arch/mips/mach-mt7620/Kconfig
@@ -0,0 +1,113 @@
+menu "MediaTek MIPS platforms"
+	depends on ARCH_MT7620
+
+config SYS_MALLOC_F_LEN
+	default 0x1000
+
+config SYS_SOC
+	default "mt7620" if SOC_MT7620
+
+choice
+	prompt "MediaTek MIPS SoC select"
+
+config SOC_MT7620
+	bool "MT7620/8"
+	select MIPS_L1_CACHE_SHIFT_5
+	help
+	  This supports MediaTek MIPS MT7620 family.
+
+endchoice
+
+choice
+	prompt "Board select"
+
+endchoice
+
+choice
+	prompt "Boot mode"
+
+config BOOT_RAM
+	bool "RAM boot"
+	depends on SUPPORTS_BOOT_RAM
+	help
+	  This builds an image that is linked to a RAM address. It can be used
+	  for booting from CFE via TFTP using an ELF image, but it can also be
+	  booted from RAM by other bootloaders using a BIN image.
+
+config BOOT_ROM
+	bool "ROM boot"
+	depends on SUPPORTS_BOOT_RAM
+	help
+	  This builds an image that is linked to a ROM address. It can be
+	  used as main bootloader image which is programmed onto the onboard
+	  flash storage (SPI NOR).
+
+endchoice
+
+choice
+	prompt "DDR2 size"
+
+config ONBOARD_DDR2_SIZE_256MBIT
+	bool "256MBit (32MByte) total size"
+	depends on BOOT_ROM
+	help
+	  Use 256MBit (32MByte) of DDR total size
+
+config ONBOARD_DDR2_SIZE_512MBIT
+	bool "512MBit (64MByte) total size"
+	depends on BOOT_ROM
+	help
+	  Use 512MBit (64MByte) of DDR total size
+
+config ONBOARD_DDR2_SIZE_1024MBIT
+	bool "1024MBit (128MByte) total size"
+	depends on BOOT_ROM
+	help
+	  Use 1024MBit (128MByte) of DDR total size
+
+config ONBOARD_DDR2_SIZE_2048MBIT
+	bool "2048MBit (256MByte) total size"
+	depends on BOOT_ROM
+	help
+	  Use 2048MBit (256MByte) of DDR total size
+
+endchoice
+
+choice
+	prompt "DDR2 chip width"
+
+config ONBOARD_DDR2_CHIP_WIDTH_8BIT
+	bool "8bit DDR chip width"
+	depends on BOOT_ROM
+	help
+	  Use DDR chips with 8bit width
+
+config ONBOARD_DDR2_CHIP_WIDTH_16BIT
+	bool "16bit DDR chip width"
+	depends on BOOT_ROM
+	help
+	  Use DDR chips with 16bit width
+
+endchoice
+
+choice
+	prompt "DDR2 bus width"
+
+config ONBOARD_DDR2_BUS_WIDTH_16BIT
+	bool "16bit DDR bus width"
+	depends on BOOT_ROM
+	help
+	  Use 16bit DDR bus width
+
+config ONBOARD_DDR2_BUS_WIDTH_32BIT
+	bool "32bit DDR bus width"
+	depends on BOOT_ROM
+	help
+	  Use 32bit DDR bus width
+
+endchoice
+
+config SUPPORTS_BOOT_RAM
+	bool
+
+endmenu