OvmfPkg/SmmCpuFeaturesLib: call CPU hot-eject handler

OvmfPkg/SmmCpuFeaturesLib: call CPU hot-eject handler

Call the CPU hot-eject handler if one is installed. The condition for
installation is (PcdCpuMaxLogicalProcessorNumber > 1), and there's
a hot-unplug request.

The handler is called from SmmCpuFeaturesRendezvousExit(), which is
in-turn called at the tail-end of SmiRendezvous() after the BSP has
signalled an SMI exit via the "AllCpusInSync" loop.

Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Aaron Young <aaron.young@oracle.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=3132
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
Message-Id: <20210312062656.2477515-8-ankur.a.arora@oracle.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>