Just like on sun8i all sun5i tablets use the same interrupt and power
gpios for their touchscreens. I've checked all known a13 fex files and
only the UTOO P66 uses a different gpio for the interrupt.

Add a touchscreen node to sun5i-reference-design-tablet.dtsi, which
fills in the necessary gpios to avoid duplication in the tablet dts files,
just like we do in sun8i-reference-design-tablet.dtsi.

This will make future patches adding touchscreen nodes to a13 tablets
simpler.
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>