mips: Add LinkIt Smart 7688 support

The LinkIt Smart 7688 modules have a MT7688 SoC with 128 MiB of RAM
and 32 MiB of flash (SPI NOR).

This patch also includes 2 targets. One is the target that can be
programmed into the SPI NOR flash and a 2nd target "xxx-ram" is
added to support loading and booting via an already running U-Boot
version. This allows easy development and testing without the
need to flash the image each time.

Signed-off-by: Stefan Roese <sr@denx.de>
[fixed and regenerated defconfig files]
Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
diff --git a/arch/mips/dts/linkit-smart-7688.dts b/arch/mips/dts/linkit-smart-7688.dts
new file mode 100644
index 0000000..df4bf90
--- /dev/null
+++ b/arch/mips/dts/linkit-smart-7688.dts
@@ -0,0 +1,46 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2018 Stefan Roese <sr@denx.de>
+ */
+
+/dts-v1/;
+
+#include "mt7628a.dtsi"
+
+/ {
+	compatible = "seeed,linkit-smart-7688", "ralink,mt7628a-soc";
+	model = "LinkIt-Smart-7688";
+
+	aliases {
+		serial0 = &uart2;
+		spi0 = &spi0;
+	};
+
+	memory@0 {
+		device_type = "memory";
+		reg = <0x0 0x08000000>;
+	};
+
+	chosen {
+		bootargs = "console=ttyS0,57600";
+		stdout-path = &uart2;
+	};
+};
+
+&uart2 {
+	status = "okay";
+	clock-frequency = <40000000>;
+};
+
+&spi0 {
+	status = "okay";
+	num-cs = <2>;
+
+	spi-flash@0 {
+		#address-cells = <1>;
+		#size-cells = <1>;
+		compatible = "spi-flash", "jedec,spi-nor";
+		spi-max-frequency = <25000000>;
+		reg = <0>;
+	};
+};
diff --git a/arch/mips/mach-mt7620/Kconfig b/arch/mips/mach-mt7620/Kconfig
index 396fbd0..ef1211d 100644
--- a/arch/mips/mach-mt7620/Kconfig
+++ b/arch/mips/mach-mt7620/Kconfig
@@ -21,6 +21,17 @@
 choice
 	prompt "Board select"
 
+config BOARD_LINKIT_SMART_7688
+	bool "LinkIt Smart 7688"
+	depends on SOC_MT7620
+	select SUPPORTS_BOOT_RAM
+	help
+	  Seeed LinkIt Smart 7688 boards have a MT7688 SoC with 128 MiB of RAM
+	  and 32 MiB of flash (SPI).
+	  Between its different peripherals there's an integrated switch with 4
+	  ethernet ports, 1 USB port, 1 UART, GPIO buttons and LEDs, and
+	  a MT7688 (PCIe).
+
 endchoice
 
 choice
@@ -110,4 +121,6 @@
 config SUPPORTS_BOOT_RAM
 	bool
 
+source "board/seeed/linkit-smart-7688/Kconfig"
+
 endmenu