regulator: Add regmap helper for ramp-delay setting

Quite a few regulator ICs do support setting ramp-delay by writing a value
matching the delay to a ramp-delay register.

Provide a simple helper for table-based delay setting.

Signed-off-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Link: https://lore.kernel.org/r/f101f1db564cf32cb58719c77af0b00d7236bb89.1617020713.git.matti.vaittinen@fi.rohmeurope.com
Signed-off-by: Mark Brown <broonie@kernel.org>