Replaced placeholder implementation of plat_set_nv_ctr for FVP
platforms by a working one.
On FVP, the mapping of region DEVICE2 has been changed from RO to RW
to prevent exceptions when writing to the NV counter, which is
contained in this region.
Change-Id: I56a49631432ce13905572378cbdf106f69c82f57
Antonio Nino Diaz