MdeModulePkg: Add the new API ResetSystem in the head file

MdeModulePkg: Add the new API ResetSystem in the head file

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=1460

Add the new API ResetSystem in the related head file so that
the consumer can use it through the combination of library
instance and head file.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Zhichao Gao <zhichao.gao@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>