speaker-test: add support for S24_LE and S24_BE

speaker-test: add support for S24_LE and S24_BE

These formats are sometimes advertised by drivers, e.g. SOF.
The format is 3 bytes packed in 32-bit container, with the MSB zeroed
out.

sample: 0x00123456

S24_LE format:
b0 56
b1 34
b2 12
b3 00

S24_BE format:
b0 00
b1 12
b2 34
b3 56

I only tested the S24_LE format with the SOF driver, S24_BE was added
for symmetry only.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>