fix(morello): add platform-specific power domain functions

fix(morello): add platform-specific power domain functions

Commit 4d8c18196378824e388cf31ef991ba8fbbb09cbf added a redistributor
power off to resolve an error on N1SDP/Morello. Prior to this fix,
turning off both cores in a cluster would cause a hang when powering
back on either core. This change introduced issues on other platforms
with a different GIC implementation, and was reverted in commit
60719e4e0965aead49d927f12bf2a37bd2629012.

This commit uses the previous fix in platform-specific implementations
of power domain off/suspend functions.

Signed-off-by: Werner Lewis <werner.lewis@arm.com>
Change-Id: Ib7689a5e08ada3862406fa92019a6f0bcfb48d79