msm: spm: Reuse msm_spm_turn_on_cpu_rail() to turn on cluster rail

msm_spm_turn_on_cpu_rail() was used to turn on the cpu rail on older
targets. Refashion this function to turn on rail for a cluster or cpus
that share the same rail.

Change-Id: Ifb6d43808b8ed534a618dd4b83634df7a3d6889a
Signed-off-by: Praveen Chidambaram <pchidamb@codeaurora.org>