MpInitLib: Move the Above1Mb vector allocation to MpInitLibInitialize

MpInitLib: Move the Above1Mb vector allocation to MpInitLibInitialize

The AP vector consists of 2 parts:
1. the initial 16-bit code that should be under 1MB and page aligned.
2. the 32-bit/64-bit code that can be anywhere in the memory with any
   alignment.

The need of part #2 is because the memory under 1MB is temporary
"stolen" for use and will "give" back after all AP wake up. The range
of memory is not marked as code page in page table. CPU may trigger
exception as soon as NX is enabled.

The part #2 memory allocation can be done in the MpInitLibInitialize.

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