regulator: tps6507x: Avoid duplicating the same mapping table for LDO2 and VDCDCx

The voltage mapping table for LDO2 is exactly the same as VDCDCx.
Thus we can use one mapping table for both LDO2 and VDCDCx instead of
duplicating the mapping table.

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