ASoC: kirkwood-dma: remove IEC958_SUBFRAME formats

The Audio block does not support IEC958 subframes as formatted by
ALSA: they're very close, but not close enough.  The formats differ
by:

3  2   2   2   1   1
1  8   4   0   6   2   8   4   0
PCUVDDDDDDDDDDDDDDDD....AAAATTTT - IEC958 subframe
PCUV0000........DDDDDDDDDDDDDDDD - Audio block format

Where P = parity, C = channel status, U = user data, V = validity,
D = sample data, A = aux, T = preamble.  As can be seen, the
position of the sample is in a different position, and the audio
block does not have the aux or preamble bits.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Mark Brown <broonie@linaro.org>