BeagleBoardPkg/ResetSystemLib: Add new API ResetSystem

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



Add a new API ResetSystem to this ResetSystemLib instance.
It only adds the basic functions from ResetSystemRuntimeDxe.
Lacking of this interface may cause link error, if some drivers
use this new API and link to this library instance.
Notes:
This library API only provide a basic function of reset. Full
function should use the instance in the MdeModulePkg and make
sure the depex driver is dispatched.

Cc: Leif Lindholm <leif.lindholm@linaro.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Liming Gao <liming.gao@intel.com>
Signed-off-by: Zhichao Gao <zhichao.gao@intel.com>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>