regulator: tps6586x: Use regulator_list_voltage_linear for dvm/ldo4/sw2

The voltage tables for dvm/ldo4/sw2 are actually linear mapping.
Thus convert dvm/ldo4/sw2 to use regulator_list_voltage_linear.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Mark Brown <broonie@linaro.org>