Declaring strings in assembler source involves a certain amount of
tedious boilerplate code in order to annotate the resulting symbol
correctly.

Encapsulating this boilerplate in a macro should help to avoid some
duplication and the occasional mistake.
Signed-off-by: NDave Martin <dave.martin@linaro.org>
Acked-by: NNicolas Pitre <nicolas.pitre@linaro.org>