i2c: riic: Add Runtime PM support

- Replace explicit clock handling by Runtime PM calls,
  - Streamline Runtime PM handling in error paths,
  - Enable Runtime PM in .probe(),
  - Disable Runtime PM in .remove(),
  - Make sure the device is runtime-resumed when disabling interrupts in
    .remove().

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Tested-by: Chris Brandt <chris.brandt@renesas.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>