fix(plat/css): fix invalid redistributor poweroff

Commit 4d8c1819
introduced an invalid redistributor power off
where we turn off the redistributor without
checking if the system power domain level is
turning off, otherwise we can turn off a
redistributor when other cores or clusters are
sharing it, also if it does indeed needs
powering off during suspend we do it twice.
This change fixes this by checking on the
system power state first then turning off
the redistributor.

Signed-off-by: Waleed Elmelegy <waleed.elmelegy@arm.com>
Change-Id: Id202bc2316ab7c516298fa33ea089ae2e221a933