regulator: ab8500: Use regulator_list_voltage_table() to look-up voltages

The regulator framework offers a generic regulator_list_voltage_table()
function which can directly look-up a regulator's voltage capabilities
using a table provided through the desc structure. This patch ensures
that information is available.

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