ARM: shmobile: r8a7778: add support I2C clock

This patch adds r8a7778 I2C clock support.
It also adds peripheral_clk which is requiested
from i2c-rcar driver

Signed-off-by: Yusuke Goda <yusuke.goda.sx@renesas.com>
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>