[ALSA] ASoC DAI capabilities labelling

This patch suggested by Takashi changes the DAI capabilities definitions
in pxa-i2s.c, at91rm9200-i2s.c, wm8731.c, wm8750.c and wm9712.c to use a
label = value style.

Signed-off-by: Liam Girdwood <liam.girdwood@wolfsonmicro.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>