ARM: efm32: update defconfig

Enable i2c driver for efm32. The other two changes are just results from
oldconfig after commits
 - 08b964ff (ARM: 8198/1: make kuser helpers depend on MMU)
 - 8357041a (of: remove /proc/device-tree)

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Olof Johansson <olof@lixom.net>