regulator: Set up GPIO for WM831x VSEL before enabling VSEL mode

If the VSEL is not in use prior to us starting up then we need to make
sure we initialise the GPIO before we push the DVS control to being done
by the GPIO.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>