mfd: Force on REGMAP for the arizona core

While the core isn't useful by itself it does depend on regmap so try to
force that on.

Reported-by: MyungJoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>