media: i2c: dw9714: add optional regulator support

Allow the dw9714 to control a regulator and adjust suspend() and resume()
to support both runtime and system pm.

Signed-off-by: Angus Ainslie <angus@akkea.ca>
Signed-off-by: Martin Kepplinger <martin.kepplinger@puri.sm>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>