msm: cpuidle: Don't disable irqs again

cpu_idle() disables irqs before calling down into the cpuidle
driver via cpuidle_idle_call(). Disabling irqs again in
msm_cpuidle_enter() is wasteful and unnecessary. It also inhibits
our ability to determine the largest irq latency when the cpu
idles for extended periods of time because the irqsoff trace is
reenabled when the irqs are disabled in msm_cpuidle_enter().

Note that we still reenable irqs before returning, as is required
by the ARM idle loop.

Change-Id: I925478d8fef88ab490959622bc68303f59cc6e79
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>