mfd: Fix build break of max77693 by adding REGMAP_I2C option

This patch add REGMAP_I2C config option to fix build break
of max77693 mfd driver because max77693 use regmap interface
for i2c communication.

drivers/mfd/max77693.c:103: error: variable 'max77693_regmap_config' has initializer but incomplete type
drivers/mfd/max77693.c:104: error: unknown field 'reg_bits' specified in initializer
drivers/mfd/max77693.c:104: warning: excess elements in struct initializer
drivers/mfd/max77693.c:104: warning: (near initialization for 'max77693_regmap_config')
drivers/mfd/max77693.c:105: error: unknown field 'val_bits' specified in initializer
drivers/mfd/max77693.c:105: warning: excess elements in struct initializer
drivers/mfd/max77693.c:105: warning: (near initialization for 'max77693_regmap_config')
drivers/mfd/max77693.c:106: error: unknown field 'max_register' specified in initializer
drivers/mfd/max77693.c:106: warning: excess elements in struct initializer
drivers/mfd/max77693.c:106: warning: (near initialization for 'max77693_regmap_config')
drivers/mfd/max77693.c: In function 'max77693_i2c_probe':
drivers/mfd/max77693.c:122: error: implicit declaration of function 'devm_regmap_init_i2c'
drivers/mfd/max77693.c:122: warning: assignment makes pointer from integer without a cast

Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Myungjoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>