arm: am335x: add support for i2c2 bus

The am335x from BeagleBone use i2c EEPROM to detect capes.
The memory is wired to i2c bus 2 therefore it need to be enabled.

Add i2c2 clock, pinmux description and pinmux enable function.

Signed-off-by: Kory Maincent <kory.maincent@bootlin.com>