control_external: Add ability to specify TLV data.

control_external: Add ability to specify TLV data.

Allow external control plugins to provide TLV data.  This allows
user-space pcms to specify dB ranges for controls.

This follows the same model as the ALSA drivers for accessing the
data.  The code is based on that implementation.  The control can
provide static data or a callback.  The data is accessed or modified
in the new snd_ctl_ext_elem_tlv callback.

Rev bump the protocol version to enable checking if an external
control supports TLV.

Signed-off-by: Dylan Reid <dgreid@chromium.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>