media: staging: atomisp: Update TODO regarding sensors

There was no specific item regarding what should be done to sensor, lens
and flash drivers. Add one, to replace the vague item denoting support
only to particular sensor, lens and flash devices.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>