feat(rdn2): update power message value to 0

Standalone MM used by RD-N2 platfrom does not have power messaging
support. Set the value to 0.

Signed-off-by: Nishant Sharma <nishant.sharma@arm.com>
Change-Id: Icdb16ea1976ce751071ce3df0e4bd86f3fb8ab8b
1 file changed