ASoC: ak4642: make arrays fs_list and ps_list static const

Don't populate the arrays fs_list and ps_list on the stack but make
them static const.  Makes the object code smaller:

Before:
   text    data     bss     dec     hex filename
  12084    4888      64   17036    428c sound/soc/codecs/ak4642.o

After:
   text    data     bss     dec     hex filename
  11883    5032      64   16979    4253 sound/soc/codecs/ak4642.o

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Mark Brown <broonie@kernel.org>