libalsa-intf: Add support for low-latency playback/recording

- Add mixer controls to support low latency playback
and recording
- Add usecase verb, modifier for low latency Rx and Tx
- Add low latency Rx and Tx capabilties in UCM

Change-Id: Icb26577f7a03886e9bdef06d9d742efced05bfee
Signed-off-by: Iliyan Malchev <malchev@google.com>