msm: pm-8x60: Check for SPM status in msm_pm_verify_cpu_pc

Verify that SPM is in sleep mode in msm_pm_verify_cpu_pc. If not, it is
possible that msm_pm_wait_cpu_shutdown could fail but acpuclock would
turn off the clocks based on the the return value of
msm_pm_verify_cpu_pc.

CRs-fixed: 376791
Change-Id: Id55019508ea9bc27106eb298e19988aecc055cac
Signed-off-by: Mahesh Sivasubramanian <msivasub@codeaurora.org>