ARM: mach-shmobile: r8a7740: add i2c support

This patch adds I2C support to r8a7740 CPU
which has lasting errata on I2C I/O pad reset.
This patch is including work-around.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>