feat(fake_host): add stub for xlat_enable_mmu_el2

This patch adds a stub for xlat_enable_mmu_el2 for the
for fake_host architecture.

Signed-off-by: Javier Almansa Sobrino <javier.almansasobrino@arm.com>
Change-Id: I7bf846bb02ca65b292a33254574f420409735799