services/spm_deprecated: update ARM platform specific asserts

services/spm_deprecated: update ARM platform specific asserts

Update some asserts that refer to #defines that only occur in
ARM platforms, preventing this code to be used on other platforms.
Instead, use a platform agnostic name, and update all the existing
users.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>