ShellPkg: force use of AARCH64 small model when building DEBUG shell

ShellPkg: force use of AARCH64 small model when building DEBUG shell

The tiny code model used by AARCH64 only supports binaries of up to
1 MB in size. Since the Shell application exceeds that when built in
DEBUG mode, make sure we build it using the small code model instead.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Tested-by: Leif Lindholm <leif.lindholm@linaro.org>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18241 6f19259b-4bc3-4df7-8a09-765794883524