i2c: sh_mobile: add device tree support

This patch enables DT support for the IIC driver
used on SH-based SoCs such as sh7722 and sh7724
among others as well as SH-Mobile SoCs such as
sh7367, sh7377, sh7372, sh73a0 and r8a7740.

Tested with out-of-tree DT support code on the
sh7372 Mackerel board.

Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>