regulator: da9121: Add header file

Add header file for Dialog Semiconductor DA9121 regulator and related
devices, mostly autogenerated from the chip design databases, and update
driver to replace local defines with those from header.

Signed-off-by: Adam Ward <Adam.Ward.opensource@diasemi.com>
Link: https://lore.kernel.org/r/3527d84448d1e6ddc0fcb883ae564880f75a6cb0.1606755367.git.Adam.Ward.opensource@diasemi.com
Signed-off-by: Mark Brown <broonie@kernel.org>