input: gpio_kbd_matrix: add column drive mode

Add an option to drive inactive columns to inactive state rather than
high impedance. This is useful if the matrix has isolation diodes for
every key, as it allows the matrix to stabilize faster and the API for
changing the pin value is more efficient than the one to change the pin
configuration.

Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>