arm64/mm: Dynamically initialize protection_map[]

Later on certain protection_map[] elements will contain a runtime variable
with FEAT_LPA2 enabled, hence preventing a successful build because of the
current static initialization method. Instead protection_map[] can just be
left static (zero) initialized, and get updated in adjust_protection_map()
with actual protection values.

Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>