regulator: s5m8767a: Support AP watchdog reset operation

The S5M8767A can't know status of ap reset.
So, After AP watchdog reset, AP can't boot normally.

Problem can be happened like below condition.
- AP Bootable lowest voltage(vdd_arm): 0.9v
- AP DVFS voltage table: 0.8v, 0.9v, 1.0v
- During AP works on lowest voltage(0.8V), watchdog reset is asserted
- AP can't boot, because vdd arm is still 0.8v

Solution
- Basic concept:
  After ap watchdog reset, GPIO configuration is changed by default value
- S5M8767A has function of voltage control with gpio (8 levels with 3 gpios)
- Set bootable voltage on level 0 -> can work with default gpio configuration
- In the probing, Change voltage control level from level 0 to level 1
- Execute normal dvfs operation on level 1
- After watchdog reset, ap gpio is set by default value
- PMIC operation mode is changed by ap reset (level1 -> level0)
- Regardless of previous vdd_arm voltage, AP always can be booted.

Signed-off-by: Sangbeom Kim <sbkim73@samsung.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

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