input: gpio_kbd_matrix: add direct access support

When the matrix is connected to consecutive pins on the same port, it's
possible to read the whole row or set the whole column in a single
operation. For the column, this is only possible if the matrix is
configured for driving unselected column, as there's no API to configure
multiple pins at the same time at the moment.

This is more efficient than checking the pins individually, and it's
particularly useful if the row or columns are driven from a GPIO port
expander.

Add some code to detect the condition and enable it automatically as
long as the hw configuration supports it.

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