Make a new PropInfo parameter that allows us to iterate all
properties. Make some new fields to set labels and names for
properties. We will be able to add more things to describe the
properties this way.
Use the Props param to simply query or set properties.
We can now make int enum properties and describe all possible
values with labels, we don't need to register types anymore.
This then makes it possible to enumerate the v4l2 controls and make
them available as control params.
Reorganize the io parameter ids and objects. Make separate enumerations
for buffer, control, input and output properties.
Add a volume output property to export-source. This is still unused
but will eventually be routed to a PropsIn io area where it can
control the volume of a mixer, for example.
Pass a spa_pod as the control io area. The pod is not supposed to
change in structure, only the values do so we can achieve the same
kind of performance as passing a single value but still allow for
more complex io area layouts to be passed later.
Add control properties to audiotestsrc for frequency and volume
and add a test program.
Add size parameter to set_io for additional checks and to make it
easy to know how much control data we can write.
