board: phytec: Add common PHYTEC SoM detection

Recent shipped PHYTEC SoMs come with an i2c  EEPROM containing
information about the hardware such as board revision and variant.
This can be used for RAM detection and loading device tree overlays
during kernel start.

Signed-off-by: Teresa Remmet <t.remmet@phytec.de>
Reviewed-by: Yannic Moog <y.moog@phytec.de>
Tested-by: Yannic Moog <y.moog@phytec.de>
Reviewed-by: Fabio Estevam <festevam@gmail.com>