ASoC: fsl-sai: using 'lsb-first' property instead of 'big-endian-data'.

The 'big-endian-data' property is originally used to indicate whether the
LSB firstly or MSB firstly will be transmitted to the CODEC or received
from the CODEC, and there has nothing relation to the memory data.

Generally, if the audio data in big endian format, which will be using the
bytes reversion, Here this can only be used to bits reversion.

So using the 'lsb-first' instead of 'big-endian-data' can make the code
to be readable easier and more easy to understand what this property is
used to do.

This property used for configuring whether the LSB or the MSB is transmitted
first for the fifo data.

Signed-off-by: Xiubo Li <Li.Xiubo@freescale.com>
Acked-by: Nicolin Chen <nicoleotsuka@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>