ARM: multi_v7_defconfig: enable I2C demultiplexer and slave eeprom

The Renesas Lager board shall be a 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>