regulator: fixed: add off-on-delay

Depends on board design, the gpio controlling regulator may
connects with a big capacitance. When need off, it takes some time
to let the regulator to be truly off. If not add enough delay, the
regulator might have always been on, so introduce off-on-delay to
handle such case.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Link: https://lore.kernel.org/r/1572311875-22880-3-git-send-email-peng.fan@nxp.com


Signed-off-by: Mark Brown <broonie@kernel.org>