[ALSA] oxygen: save register writes

Save the written values of all CMI8788 and AC97 registers and of some of
the DAC/ADC registers so that it is possible to restore the register
state later.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>