regulator: tps51632: Add tps51632 regulator driver

The TPS51632 is a driverless step down controller with
serial control. Advanced features such as D-Cap+
architecture with overlapping pulse support and OSR
overshoot reduction provide fast transient response,
lowest output capacitance and high efficiency.
The TPS51632 supports both I2C and DVFS interfaces
(through PWM) for dynamic control of the output voltage
and current monitor telemetry.
Add regulator driver for TPS51632.

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