cpufreq: schedutil: irq-work and mutex are only used in slow path

Execute the irq-work specific initialization/exit code only when the
fast path isn't available.

Change-Id: I490d4de28393360984c77435db7fadeda53e454f
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Git-commit: 21ef57297b15a49b0c4dd4e7135c1a08e9a29a1c
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


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