regulator: lp87565: Add support for lp87565 PMIC regulators

The regulators set consists of 4 BUCKs. The output
voltages are configurable and are meant to supply power to the
main processor and other components. The ramp delay is configurable
for all BUCKs. The BUCKs can be configured in single phase or
multiphase modes.

Signed-off-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>