[ALSA] cs4231 header split

This patch splits the cs4231.h file into two parts:
- cs4231-regs.h which contain register constants and macros
- cs4231.h which includes the above and contain rest of the definitions
This will allow to share register definitions between x86 ISA cs4231
and SPARC cs4231.

Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>