ALSA: hdspm - Create TCO readout function

This patch separates the TCO bits from snd_hdspm_proc_read_madi(), so
the new function can later be shared between MADI and AES32 cards.

It's essentially only moving code around, no new functionality.

Signed-off-by: Adrian Knoth <adi@drcomp.erfurt.thur.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>