Update s5m8767 regulator driver

Hi!

As samsung s5m8767a pmic is revisioned,
I update regulator driver for s5m8767a.

Revision & modification items:
- Modify ramp delay value
- Modify reset value
- Support AP watchdog reset
- Use set_voltage_sel function
- Fix the minor bug

[PATCH 1/5] regulator: Remove buck initialization in driver probing [PATCH 2/5] regulator: Fix the problem of the division by null [PATCH 3/5] regulator: Modify ramp_delay value
[PATCH 4/5] regulator: Replace set_voltage with set_voltage_sel [PATCH 5/5] regulator: Support AP watchdog reset operation for s5m8767a

Thanks,
Sangbeom.