On ARM platforms, the maximum size of the address space is limited
to 32-bits as defined in arm_def.h. In order to access DRAM2, which
is defined beyond the 32-bit address space, the maximum address space
is increased to 36-bits in AArch64. It is possible to increase the
virtual space for AArch32, but it is more difficult and not supported
for now.

NOTE - the actual maximum memory address space is platform dependent
and is checked at run-time by querying the PARange field in the
ID_AA64MMFR0_EL1 register.

Change-Id: I6cb05c78a63b1fed96db9a9773faca04a5b93d67
Signed-off-by: Roberto Vargas <roberto.vargas@arm.com>