regulator: tps62360: support force PWM mode via regulator mode

Change the mechanism of enabling the force PWM mode through
regulator set mode. This can be dynamically configured now.
In the REGULATOR_MODE_FAST the force PWM is enabled and in
REGULATOR_MODE_NORMAL the force PWM is disabled.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>