fix(drivers/arm/rse) force rse comms embed in RME

RSE COMMS pointer access protocol is not support with RME enabled as
pointers could have NS, S, RT or RM access permissions and this is not
currently supported on RSS. Therefore when RME is enabled rse comms
should always use the embed protocol.

Change-Id: Ice48b14ae139d5bcfa607a36bf901a0f68b0400c
Signed-off-by: Joel Goddard <joel.goddard@arm.com>
Signed-off-by: Nishant Sharma <nishant.sharma@arm.com>