mips: mt76xx: linkit-smart-7688: Misc updates to dts/config/defconfig

These misc updates include the following changes:
- Change baudrate from 57600 to 115200
- Enable MIPS_BOOT_CMDLINE_LEGACY
- Enable FIT support
- Enable ethernet support
- Enable SPI support
- Enable GPIO support
- Change max image size from 0x40000 to 0x80000

A note about the baudrate change:

The original Mediatek U-Boot version used 57600 baud. Lets move to a
more common and faster speed of 115200 baud. And remove the "console="
property from the DT as its not needed.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
diff --git a/include/configs/linkit-smart-7688.h b/include/configs/linkit-smart-7688.h
index 78efa23..3bae92d 100644
--- a/include/configs/linkit-smart-7688.h
+++ b/include/configs/linkit-smart-7688.h
@@ -38,7 +38,7 @@
 #define CONFIG_SYS_MONITOR_BASE		CONFIG_SYS_TEXT_BASE
 
 /* Environment settings */
-#define CONFIG_ENV_OFFSET		0x40000
+#define CONFIG_ENV_OFFSET		0x80000
 #define CONFIG_ENV_SIZE			(16 << 10)
 #define CONFIG_ENV_SECT_SIZE		(64 << 10)