regulator: Add 'start-up time' to fixed voltage regulators

Add a field to specify a delay for the start-up time of
a fixed voltage regulator.

Signed-off-by: Adrian Hunter <adrian.hunter@nokia.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>