Add support for ADP5055 triple buck regulator.

Merge series from Alexis Czezar Torreno <alexisczezar.torreno@analog.com>:

Introduce a regulator driver support for ADP5055. The device combines 3
high performance buck regulators in a 43-termminal land grid array
package. The device enables direct connection to high input voltages up
to 18V with no preregulator. Channel 1 and 2 deliver a programmable
output current of 3.5A or 7.5A or provide a single output with up to 14A
in parallel operation. Channel 3 has a programmable output current of
1.5A or 3A.