am335x: Register the I2C controllers if DM_I2C is used.

If DM_I2C is used , the I2C controllers must be registered as U_BOOT_DEVICE
because OF_CONTROL is not used in the SPL.

Signed-off-by: Jean-Jacques Hiblot <jjhiblot@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Heiko Schocher <hs@denx.de>