Add Beaglebone Enhanced support

The "Beaglebone Enhanced" by Sancloud is based on the Beaglebone Black,
but with the following differences:

 * Gigabit capable PHY
 * Extra USB hub, optional i2c control
 * lps3331ap barometer connected over i2c
 * MPU6050 6 axis MEMS accelerometer/gyro connected over i2c
 * 1GiB DDR3 RAM
 * RTL8723 Wifi/Bluetooth connected over USB

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>
Reviewed-by: Tom Rini <trini@konsulko.com>