Although S5P4418 and 4412 look very similar, the difference in GPIO is very big. It is almost another system.
The GPIOs of 4412, 6410, 210, 310, etc. are similar, and there are pins dedicated to matrix keyboards, so the matrix keyboard driver can use samsung_keypad.c, and you can configure it in menuconfig.
However, S5P4418 GPIO is not specifically designated as a matrix keyboard pin. It is sufficient to use a general matrix keyboard to drive matrix_keypad.c, but note that the row line needs to be set to pull up in cfg_gpio.h, and these GPIOs cannot be used for other purposes. .