UefiCpuPkg/MpInitLib: Add code to initialize MapMask

In function CreatePageTable(), add code to initialize MapMask to
MAX_UINT64. When creating new page table or map non-present range
to present, all attributes should be provided.

Signed-off-by: Dun Tan <dun.tan@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Reviewed-by: Ray Ni <ray.ni@intel.com>
Cc: Rahul Kumar <rahul1.kumar@intel.com>
Tested-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>