Rename the reference-design-tablet touchscreen node from gsl1680 to
touchscreen, all? tablets seem to use the same power and interrupt
gpio-s, but not all tablets use a gsl1680 controller making the
gsl1680 name somewhat misleading.

Also move the reg and compatible property to the actual tablet dts
as they may differ per tablet.
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>