ARM: dts: Add am335x-bonegreen

ARM: dts: Add am335x-bonegreen

SeeedStudio BeagleBone Green (BBG) is clone of the BeagleBone Black (BBB) minus
the HDMI port and addition of two Grove connectors (i2c2 and usart2).

This board can be identified by the 1A value after A335BNLT (BBB) in the at24 eeprom:
1A: [aa 55 33 ee 41 33 33 35  42 4e 4c 54 1a 00 00 00 |.U3.A335BNLT....|]

http://beagleboard.org/green
http://www.seeedstudio.com/wiki/Beaglebone_green

Signed-off-by: Robert Nelson <robertcnelson@gmail.com>
CC: Tony Lindgren <tony@atomide.com>
CC: Jason Kridner <jkridner@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>