mfd: Add Renesas Synchronization Management Unit (SMU) support

Add support for ClockMatrix(TM) and 82P33xxx families of timing
and synchronization devices. The access interface can be either
SPI or I2C. Currently, it will create 2 types of MFD devices,
which are to be used by the corresponding rsmu character device
driver and the PTP hardware clock driver, respectively.

Signed-off-by: Min Li <min.li.xe@renesas.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>