mfd: arizona: Add support for WM8280/WM8281

This adds support for the Wolfson Microelectronics WM8280 and WM8281
codecs.

Signed-off-by: Richard Fitzgerald <rf@opensource.wolfsonmicro.com>
Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
[Lee: Minor fixup to remove potentially uninitialised variable. ]
Signed-off-by: Lee Jones <lee.jones@linaro.org>