hwdriver: introduce SR_CONF_PROBE_NAMES config key (scan option)

hwdriver: introduce SR_CONF_PROBE_NAMES config key (scan option)

Device drivers assign a fixed set of probe names during scan. Users can
rename previously created channels in the GUI as well as in the CLI,
though this is tedious, and depends on the application, as well as
depends on the names which the driver initially used to assign. Manual
assignment of protocol decoder inputs to device channel names is as
tedious.

Introduce the SR_CONF_PROBE_NAMES scan option, which assigns the user
provided names to the device's probes during scan already (for those
drivers which support the option). This commit declares the config key
but does not affect any driver yet.