regulator: core: Support table based mapping in regulator_set_voltage_time_sel

For table based mapping, we can calculate voltage difference by below equation:
abs(rdev->desc->volt_table[new_selector] - rdev->desc->volt_table[old_selector])

Thus we can make regulator_set_voltage_time_sel work for table based mapping.

regulator_set_voltage_time_sel() only supports linear or table based mapping.
In case it is misused, also warn if neither linear nor table based mapping
is used with regulator_set_voltage_time_sel().

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>