ARM: dts: am57xx-beagle-x15: Add eeprom information

Add EEPROM at 0x50 that describes the board configuration.
This is useful for userspace programs that may need to check board
revision and other similar information.

Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>