ARM: shmobile: defconfig: enable I2C demultiplexer and slave eeprom

The Lager board shall be the reference platform for the runtime I2C IP
core switcher and for I2C slave support. Enable the needed drivers for
this.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>