Input: edt-ft5x06 - select REGMAP_I2C

After starting to use regmap API to access registers the edt-ft5x06
driver depends on symbols provided by REGMAP_I2C:

edt-ft5x06.o: in function `edt_ft5x06_ts_probe':
edt-ft5x06.c:1154: undefined reference to `__regmap_init_i2c'
edt-ft5x06.o: in function `edt_ft5x06_ts_identify':
edt-ft5x06.c:897: undefined reference to `__regmap_init_i2c'

Make sure support for I2C regmap is actually selected by adding this
dependency to Kconfig.

Fixes: 9dfd9708

 ("Input: edt-ft5x06 - convert to use regmap API")
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Link: https://lore.kernel.org/r/ZDRBExF1xmxalMZc@makrotopia.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>