SignedCapsulePkg: fix AARCH64 build
    
    BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=2252
    
    Add NULL library resolution of CompilerIntrinsicsLib and
    BaseStackCheckLib for AARCH64 as well as ARM in order to
    fix "undefined reference to `memcpy'" build errors.
    
    Cc: Jiewen Yao <jiewen.yao@intel.com>
    Cc: Chao Zhang <chao.b.zhang@intel.com>
    Cc: Laszlo Ersek <lersek@redhat.com>
    Signed-off-by: Leif Lindholm <leif.lindholm@linaro.org>
    Reviewed-by: Jiewen Yao <Jiewen.yao@intel.com>