msm: pm-8x60: Disable premption in msm_pm_enable_retention

msm_pm_retention_enable() makes smp_call_function_many to ensure that
when a retention is disabled, the cores come out of its low power mode.
Per the smp_call_function_many documentations, preemption should be
disabled before invoking the API.

CRs-fixed: 463188
Change-Id: I4ae9137e8f8e821af729becd0e2d6e6886d5e787
Signed-off-by: Mahesh Sivasubramanian <msivasub@codeaurora.org>