media: media api: Try to make enum usage clearer

This clarifies which side of the calls is responsible for doing what to
which parts of the struct. It also expands the terse description of the
access algorithm into more prose-like, active voice description, which
trades conciseness for ease of comprehension.

Fixed: typo "format" -> "frame size" in enum-frame-size
Added: no holes in the enumeration
Added: enumerations per what?
Added: who fills in what in calls
Changed: "given" -> "specified"

[Sakari Ailus: Rewrap text]

Signed-off-by: Dorota Czaplejewicz <dorota.czaplejewicz@puri.sm>
Acked-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>