ptp: clockmatrix: use rsmu driver to access i2c/spi bus

rsmu (Renesas Synchronization Management Unit ) driver is located in
drivers/mfd and responsible for creating multiple devices including
clockmatrix phc, which will then use the exposed regmap and mutex
handle to access i2c/spi bus.

Signed-off-by: Min Li <min.li.xe@renesas.com>
Signed-off-by: David S. Miller <davem@davemloft.net>