pmic: pca9450: Add regulator driver

pmic: pca9450: Add regulator driver

Add PCA9450 regulator driver. This is complementary driver for the BUCKn
and LDOn regulators provided by the PCA9450 PMIC driver. Currently the
driver permits reading the settngs and configuring the BUCKn and LDOn
regulators.

Reviewed-by: Fabio Estevam <festevam@denx.de>
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Fabio Estevam <festevam@denx.de>
Cc: Peng Fan <peng.fan@nxp.com>
Cc: Stefano Babic <sbabic@denx.de>