The driver contains at least six similar functions that change only a
single bit in the control register, only the bit position varies.

This patch implements a generic function to toggle a certain bit
position that will be used to replace the old code.
Signed-off-by: NAdrian Knoth <adi@drcomp.erfurt.thur.de>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>