regulator: TPS65910: Fix VDD1/2 voltage selector count

Count of selector voltage is required for regulator_set_voltage
to work via set_voltage_sel. VDD1/2 currently have it as zero,
so regulator_set_voltage won't work for VDD1/2.
Update count (n_voltages) for VDD1/2.

Output Voltage = (step value * 12.5 mV + 562.5 mV) * gain

With above expr, number of voltages that can be selected is
step value count * gain count

constant for gain count will be called VDD1_2_NUM_VOLT_COARSE

existing constant for step value count is VDD1_2_NUM_VOLTS,
use VDD1_2_NUM_VOLT_FINE instead to make clear that step value
is not the only component in deciding selectable voltage count

Signed-off-by: Afzal Mohammed <afzal@ti.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>