ASoC: Add compress_type as a member to snd_soc_codec

We need to keep a copy of the compress_type supplied by the codec driver
so that we can override it if necessary with whatever the machine driver
has provided us with.  The reason for not modifying the codec->driver
struct directly is that ideally we'd like to keep it const.

Adjust the code in soc-cache and soc-core to make use of the compress_type
member in the snd_soc_codec struct.

Signed-off-by: Dimitris Papastamos <dp@opensource.wolfsonmicro.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>