UefiCpuPkg/PiSmmCpuDxeSmm: Avoid allocate Token every time

UefiCpuPkg/PiSmmCpuDxeSmm: Avoid allocate Token every time

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2388

Token is new introduced by MM MP Protocol. Current logic allocate Token
every time when need to use it. The logic caused SMI latency raised to
very high. Update logic to allocate Token buffer at driver's entry point.
Later use the token from the allocated token buffer. Only when all the
buffer have been used, then need to allocate new buffer.

Reviewed-by: Ray Ni <ray.ni@intel.com>
Signed-off-by: Eric Dong <eric.dong@intel.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>