configs/rdn2: enable MPAM

Latest WinPE releases access MPAM system registers. If the platform on
which WinPE is tested doesn't have MPAM enabled (or traps disabled from
EL3), there would be a crash on access. As RD-N2 is a platform on which
WinPE is tested, enable MPAM on the platform.

Signed-off-by: Rohit Mathew <Rohit.Mathew@arm.com>
Change-Id: I7f6ac37aa8e99b9dc2d33083d901da7bef6e5623