Input: tegra-kbc - add support for rows/columns configuration from dt

The NVIDIA's Tegra KBC has maximum 24 pins to make matrix keypad.
Any pin can be configured as row or column. The maximum column pin
can be 8 and maximum row pin can be 16.

Remove the assumption that all first 16 pins will be used as row
and remaining as columns and Add the property for configuring pins
to either row or column from DT. Update the devicetree binding
document accordingly.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>