cpufreq: Introduce cpufreq_driver_test_flags()

Add a helper function to test the flags of the cpufreq driver in use
againt a given flags mask.

In particular, this will be needed to test the
CPUFREQ_NEED_UPDATE_LIMITS cpufreq driver flag in the schedutil
governor.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>