MdeModulePkg: add LockBoxNullLib for !IA32/X64 in .dsc

MdeModulePkg: add LockBoxNullLib for !IA32/X64 in .dsc

Commit 05fd2a926833
("MdeModulePkg/NvmExpressPei: Consume S3StorageDeviceInitList LockBox")
added a dependency on LockBoxLib to NvmExpressPei, causing builds using
MdeModulePkg.dsc to fail on architectures other than IA32/X64 with
missing reference to
gEfiMdeModulePkgTokenSpaceGuid.PcdDxeIplSwitchToLongMode.

Add a resolution for LockBoxNullLib for ARM/AARCH64 to restore builds.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Leif Lindholm <leif.lindholm@linaro.org>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Hao Wu <hao.a.wu@intel.com>