cpuidle, OMAP3: Push RCU-idle into driver

Doing RCU-idle outside the driver, only to then teporarily enable it
again before going idle is suboptimal.

Notably the cpu_pm_*() calls implicitly re-enable RCU for a bit.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Tony Lindgren <tony@atomide.com>
Tested-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: Tony Lindgren <tony@atomide.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://lore.kernel.org/r/20230112195539.883561913@infradead.org