drivers: pinctrl: pfc_rcar: add dummy IPSR flag to pinctrl driver

Add a dummy IPSR flag to the RCar PFC driver. It is necessary
to ensure that the driver sets the 'peripheral' bit (the driver
resets this bit during the first call of 'pfc_rcar_set_gpsr') for
a pin that doesn't have a pin function defined in IPSR, but always
acts as a 'peripheral', for example, the MMC pins on the Spider
board.

Signed-off-by: Mykola Kvach <mykola_kvach@epam.com>