tinyalsa: Add missing handler for SNDRV_CTL_ELEM_TYPE_BYTES values

Change-Id: Ia1ef4d80b32a4ce2c7a3c78af1abb672cdebdf42
Signed-off-by: Vitaly Rodionov <vitaly.rodionov@wolfsonmicro.com>
Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
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.