KabylakeOpenBoardPkg/KabylakeRvp3: Add PeiSerialPortlibSpiFlash to build

REF:https://bugzilla.tianocore.org/show_bug.cgi?id=3307



This library is part of KabylakeOpenBoardPkg but is currently not
built anywhere. This change adds the library to the KabylakeRvp3
build to ensure it can always build properly if not linked
elsewhere.

Cc: Chasel Chiu <chasel.chiu@intel.com>
Cc: Nate DeSimone <nathaniel.l.desimone@intel.com>
Signed-off-by: Michael Kubacki <michael.kubacki@microsoft.com>
Reviewed-by: Chasel Chiu <chasel.chiu@intel.com>
Reviewed-by: Nate DeSimone <nathaniel.l.desimone@intel.com>
Tested-by: Benjamin Doron <benjamin.doron00@gmail.com>