cpufreq: dt: allow driver to boot automatically

by adding the missing MODULE_ALIAS(), cpufreq-dt
can be autoloaded by udev/systemd.

Signed-off-by: Felipe Balbi <balbi@ti.com>
Acked-by: Nishanth Menon <nm@ti.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>