pcm: support S24_LE format

S24_LE is 24 bit audio in a 32 bit sample size. Also
make the pcm_format_to_bits() function part of the API
since it will be required for tinycap.
tinycap: support 24 bit capture
tinymix: only print mixer name for full mixer dump
tinymix: Add support for setting/getting a binary control

To set a binary control, we need to pass in the filename
that contains the payload we want to set.  At the moment there
is a 512 byte limit imposed by ALSA so respect that.

For binary controls, use mixer_ctl_get_bytes() to get the
payload at once instead of looping over each byte.