WhitleyOpenBoardPkg: Add SpiFlashCommonLib.h

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



Adds the header file to WhitleyOpenBoardPkg since it was removed from
MinPlatformPkg.

Cc: Isaac Oram <isaac.w.oram@intel.com>
Cc: Nate DeSimone <nathaniel.l.desimone@intel.com>
Cc: Chasel Chiu <chasel.chiu@intel.com>
Signed-off-by: Michael Kubacki <michael.kubacki@microsoft.com>
Reviewed-by: Isaac Oram <Isaac.w.oram@intel.com>
Reviewed-by: Nate DeSimone <nathaniel.l.desimone@intel.com>