media: v4l: async: Rename async nf functions, clean up long lines

Rename V4L2 async notifier functions, replacing "notifier" with "nf" and
removing "_subdev" at the end of the function names adding subdevs as you
can only add subdevs to a notifier. Also wrap and otherwise clean up long
lines.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Rui Miguel Silva <rmfrfs@gmail.com> (imx7)
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>