regulator: twl: Provide of_map_mode for twl4030

of_map_mode is needed so to be possible to set initial regulators mode from
the board DTS. Otherwise, for DT boot, regulators are left in their default
state after reset/reboot. Document device specific modes as well.

Signed-off-by: Ivaylo Dimitrov <ivo.g.dimitrov.75@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>