ASoC: davinci-mcasp: Convert the context save/restore to use array

Instead of individual values use an array to store the registers need to be
saved on suspend and restored on resume.
It is going to be easier to add more registers to save and restore.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>