fix(n1sdp): 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: I52c463646c494fe931ff4ce47afb940a56978fcd
diff --git a/plat/arm/board/n1sdp/platform.mk b/plat/arm/board/n1sdp/platform.mk
index 9c0cc02..bd62614 100644
--- a/plat/arm/board/n1sdp/platform.mk
+++ b/plat/arm/board/n1sdp/platform.mk
@@ -47,6 +47,7 @@
 				${INTERCONNECT_SOURCES}			\
 				${N1SDP_GIC_SOURCES}			\
 				${N1SDP_BASE}/n1sdp_bl31_setup.c	\
+				${N1SDP_BASE}/n1sdp_pm.c		\
 				${N1SDP_BASE}/n1sdp_topology.c	        \
 				${N1SDP_BASE}/n1sdp_security.c		\
 				drivers/arm/css/sds/sds.c