drivers: Add and use STD_CONFIG_LIST().

drivers: Add and use STD_CONFIG_LIST().

This ensures consistent handling of the SR_CONF_SCAN_OPTIONS and
SR_CONF_DEVICE_OPTIONS (with sdi NULL or non-NULL) config keys
and also reduces copy-pasted boilerplate in the drivers a bit.

This function does not handle channel-group specific items, that's
very driver-specific and thus left to the individual drivers.

Also move some generic checks and error messages from the drivers into
the sr_config_list() wrapper.