rcar/module: add PMIC DDR BKUP Mode to Power Domain Protocol

Call POWER_STATE_SET with domain ID and power state:

 - domain ID:
    20(0x14) :  PMIC DDR BACKUP MODE

 - power state:
    ON : to set "PMIC's DDR BKUP Mode" on.
    OFF: to set "PMIC's DDR BKUP Mode" off.

Signed-off-by: Tsutomu Muroya <tsutomu.muroya.jy@bp.renesas.com>
Signed-off-by: Nicolas Royer <nroyer@baylibre.com>