regulator: act8865: support output voltage by VSET2[] bits

For the step-down DC/DC regulators, the output voltage is
selectable by setting VSEL pin that when VSEL is low, output
voltage is programmed by VSET1[] bits, and when VSEL is high,
output voltage is programmed by VSET2[] bits.

The DT property "active-semi,vsel-high" is used to specify
the VSEL pin at high on the board.

Signed-off-by: Wenyou Yang <wenyou.yang@atmel.com>
Reviewed-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>