boards: Change dependency for I2C on i.mx rt boards

Changes dependency for I2C so that it's enabled if kscan is enabled.
This is to allow the kscan_ft5336 sample to run.
Note: LVGL has KSCAN as a dependency.
Applies to the mimxrt10{50,60,64}_evk boards.

Signed-off-by: Mark Olsson <mark@markolsson.se>