UefiCpuPkg/MpInitLib: fix incorrect stack top init for cpu0

UefiCpuPkg/MpInitLib: fix incorrect stack top init for cpu0

As the name suggests, CpuMpData->CpuInfoInHob[0].ApTopOfStack must be init
to the top of stack. But the MpInitLibInitialize() passed the base address
of stack to InitializeApData(), which is not correct. Although this stack
is not used for BSP, it's should be fixed in case of misunderstanding and
future possible code changes.

Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jian J Wang <jian.j.wang@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Eric Dong <eric.dong@intel.com>