ARM: multi_v7_defconfig: configure I2C driver built-in

PMIC often require the I2C bus, and the PMIC regulators might be
necessary to power on eMMC/SD-card or other supplies required
for successful boot. Make sure I2C driver for i.MX devices is
built-in.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>