regulator: max8998 BUCK1/2 voltage change with use of GPIOs

regulator: max8998 BUCK1/2 voltage change with use of GPIOs

max8998_pmic_probe:
- modified to check if valid pins are defined at platform
data
- maximal voltage values (predefined at platform data) are uploaded to
max8998 device

max8998_set_voltage_buck:
- BUCK1/2 voltages change between values already defined
- Checks if valid GPIO pins are passed from platform data
- If requested voltage cannot be satisfied from already defined values,
then one of free slots is used
- Predefined maximum voltages (as defined at platform data) are always
available

Signed-off-by: Lukasz Majewski <[email protected]>
Signed-off-by: Kyungmin Park <[email protected]>
Acked-by: Mark Brown <[email protected]>
Acked-by: Liam Girdwood <[email protected]>
Signed-off-by: Samuel Ortiz <[email protected]>