UefiCpuPkg/PiSmmCpuDxeSmm: Replace mIsBsp by mBspApicId check

This patch is to replace mIsBsp by mBspApicId check.
mIsBsp becomes the local variable (IsBsp), then it can be
checked dynamically in the function. Instead, we define the
mBspApicId, which is to record the BSP ApicId used for
compare in SmmInitHandler. With this change, SmmInitHandler
can be run in parallel during SMM init.

Note:
This patch is the per-prepared work by refining the
SmmInitHandler, then, we can do the next step to
combine 2 SMIs (gcSmmInitTemplate & gcSmiHandlerTemplate)
into one (gcSmiHandlerTemplate), the new SMI handler
will call the SmmInitHandler in parallel to do the init.

Cc: Eric Dong <eric.dong@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Zeng Star <star.zeng@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Rahul Kumar <rahul1.kumar@intel.com>
Signed-off-by: Jiaxin Wu <jiaxin.wu@intel.com>
Reviewed-by: Ray Ni <ray.ni@intel.com>
Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>