regulator: ab8500: Further populate initialisation registers

This patch supplies access to some extra settings provided by the
AB8500 regulator device. We also update some of the existing
initialisation values in accordance with internal ST-Ericsson code
submissions. This single patch was originally a collection of updates
which have been squashed together to aid with clarity.

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>