ARM64: mm: Raise MAX_ORDER for 64KB pages and THP.

The buddy allocator has a default MAX_ORDER of 11, which is too
low to allocate enough memory for 512MB Transparent HugePages if
our base page size is 64KB.

This patch introduces MAX_ZONE_ORDER and sets it to 14 when 64KB
pages are used in conjuction with THP, otherwise the default value
of 11 is used.

Signed-off-by: Steve Capper <steve.capper@linaro.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>