feat(plat/rcar3): add SYSCEXTMASK bit set/clear in scu_power_up

Added the process of SYSECEXTMASK bit set/clear for following
power Resume/Shutoff flow.

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: I71ed22840a42e7ab7d87bfd4241eec6f5ddb129b
2 files changed