media: ov2740: Add regulator support

On some designs the regulators for the AVDD / DOVDD / DVDD power rails
are controlled by Linux.

Add support to the driver for getting regulators for these 3 rails and
for enabling these regulators when necessary.

The datasheet specifies a delay of 0ns between enabling the regulators,
IOW they can all 3 be enabled at the same time. This allows using the bulk
regulator API.

The regulator core will provide dummy regulators for the 3 power-rails
when necessary.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Ricardo Ribalda <ribalda@chromium.org>
Tested-by: Stanislaw Gruszka <stanislaw.gruszka@linux.intel.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>