IntelFrameworkPkg/FrameworkUefiLib: implement EfiEventGroupSignal

IntelFrameworkPkg/FrameworkUefiLib: implement EfiEventGroupSignal

This patch follows the implementation seen in MdePkg's UefiLib instance,
so that FrameworkUefiLib also covers the UefiLib.h library class header
completely.

Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Jeff Fan <jeff.fan@intel.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Suggested-by: Jordan Justen <jordan.l.justen@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>