media: atomisp: ov2680: Add runtime-pm support

Add runtime-pm support. This is a preparation patch for letting
ACPI deal with the regulators and clocks instead of the DIY code
in atomisp_gmin_platform.c.

Reviewed-by: Andy Shevchenko <andy@kernel.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>