drivers: mfd: use single read and write mode for i2c regmap config

i2c doesn't support bulk read and write. Enable the single read and write
option in regmap configuration for audio codec to operate correctly in
i2c mode.

Change-Id: I8d27826fe634c660c848a2a8db78f8a31ba16ed0
Signed-off-by: Deven Patel <cdevenp@codeaurora.org>