ShellPkg: Add missing header files

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jaben Carsey <Jaben.Carsey@intel.com>
Reviewed-by: Daryl McDaniel daryl.mcdaniel@intel.com


git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@15262 6f19259b-4bc3-4df7-8a09-765794883524