Change crt0.S to save the app return value on the stack

This can be read by the SMC driver in the first word of the stack.
That is, at _stack_ptr - 4, or ORIGIN(DTCM) + length(DTCM) - 68.

Bug: 201363931

Change-Id: I930c0ce92f26cbfbf3b2628dc85eb8bbfdb5097e
1 file changed