i2c: i2c-sh_mobile: support I2C hardware block with a faster operating clock

On newer SH-/R-Mobile SoCs, a clock supply to the I2C hardware block,
which is used to generate the SCL clock output, is getting faster than
before, while on the other hand, the SCL clock control registers, ICCH
and ICCL, stay unchanged in 9-bit-wide (8+1).

On such silicons, the internal SCL clock counter gets incremented every
2 clocks of the operating clock.

This patch makes it configurable through platform data.

Signed-off-by: Shinya Kuribayashi <shinya.kuribayashi.px@renesas.com>
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>