msm: spm: stub out functions using spm version

msm_spm_turn_on_cpu_rail is only defined for SPM_V2. Stub out this
function for SPM_V1 so that targets using this CONFIG can compile.

Change-Id: Ia0377aa6797369f13660dad10cc6d954dea3647a
Signed-off-by: Syed Rameez Mustafa <rameezmustafa@codeaurora.org>