cpufreq: rewrite cpufreq_driver->flags using shift operator

Currently cpufreq_driver's flags are defined directly using 0x1, 0x2, 0x4, 0x8,
etc.. As the list grows it becomes less readable..

Use bitwise shift operator << to generate these numbers for respective
positions.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>