fix(plat/rcar3): fix SYSTEM_OFF processing for R-Car D3

Fixed an issue where the CPU and Cluster could not be turned OFF
when the SYSTEM_OFF has executed.

Signed-off-by: Hideyuki Nitta <hideyuki.nitta.jf@hitachi.com>
Signed-off-by: Toshiyuki Ogasahara <toshiyuki.ogasahara.bo@hitachi.com>
Signed-off-by: Yoshifumi Hosoya <yoshifumi.hosoya.wj@renesas.com>
Change-Id: Id476f815b58246ae0574c04ccb3eb201d09039b9