Config value is changed from CONFIG_ARM64_PGTABLE_LEVELS
to CONFIG_PGTABLE_LEVELS in 3.18.
vmemmap is shifted to base addr (0x80000000):
commit ab754494cbe4dd44a9e1354b3d93c8d5d5139aad

Change-Id: Ib6fa6e1b780db5117f8a750003216794d9cedeea