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/board/seeed/linkit-smart-7688/Kconfig b/board/seeed/linkit-smart-7688/Kconfig
new file mode 100644
index 0000000..a9d6328
--- /dev/null
+++ b/board/seeed/linkit-smart-7688/Kconfig
@@ -0,0 +1,12 @@
+if BOARD_LINKIT_SMART_7688
+
+config SYS_BOARD
+	default "linkit-smart-7688"
+
+config SYS_VENDOR
+	default "seeed"
+
+config SYS_CONFIG_NAME
+	default "linkit-smart-7688"
+
+endif