soc: qcom: spm: add SCM probe dependency

Check for SCM availability before attempting to use SPM. SPM probe will
fail otherwise.

Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: John Crispin <john@phrozen.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>