ASoC: arizona: Implement stability check for EQ coefficients

Specifying unstable coefficients for the EQ can have a severe impact on
the audio. This patchs adds a stability check on the coefficients
written to the EQ, for this it is necessary to merge the mode control
and the coefficients as some coefficients may only be unstable with a
certain mode setting so it is ideal if these are always updated in sync.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>