Issue description: On some pmics, the policy enable for thermal alerts
refers to different bit fields of the same registers, whereas on other
pmics, the policy enable refers to the same bit field on different
registers. Previous implementation did not provide the flexibility for
supporting the first approach.

Solution: Modified the policy enable function to take bit field as well.
The use of bit field is left to the pmic specific opregion driver.
Signed-off-by: Yegnesh Iyer <yegnesh.s.iyer@intel.com>
Signed-off-by: Bin Gao <bin.gao@intel.com>
Reviewed-by: Aaron Lu <aaron.lu@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>