media: i2c: Add pm_runtime support to ov7251

Add pm_runtime support to the ov7251 driver.

Signed-off-by: Daniel Scally <djrscally@gmail.com>
Acked-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>