feat(fvp): increase MAX_XLAT_TABLES entries for DRTM support

DRTM implementation maps the DLME data region provided by the
DCE-preamble in BL31, hence increased MAX_XLAT_TABLES entries
count.

Signed-off-by: Manish V Badarkhe <manish.badarkhe@arm.com>
Signed-off-by: Lucian Paul-Trifu <lucian.paultrifu@gmail.com>
Change-Id: I5f0ac69e009c4f81d3590fdb1f4c0a7f73c5c99d