i2c: rcar: disable PM in multi-master mode

In multi master mode, the IP core needs to be always active for
arbitration reasons. Get the config from DT and set up PM depending on
the config.

Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>