arm64: Mask out 16KB granule in MMFR register

Memory model feature register specifies the supported
page granules. Some ARM cpus may have support for
16KB granules.
However currently we donot support 16KB pages sizes.
Explicitly mask off that capability if advertised by
the cpu.

Change-Id: I7daf3f179a5ce103aec7cf103ac198cf64800543
Signed-off-by: Hanumant Singh <hanumant@codeaurora.org>