ARM: shmobile: Include i2c-shmobile.c in shmobile_defconfig

Many SoCs include I2C controller instances compatible with
the i2c-shmobile.c driver. To increase hardware support enable
the driver in the shmobile_defconfig multiplatform configuration.

Signed-off-by: Magnus Damm <damm@opensource.se>
Acked-by: Wolfram Sang <wsa@the-dreams.de>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>