ARM: dts: sun8i: reference-design-tablet: ldo_io1 is vcc-touchscreen

On some Q8 and other tablets ldo_io1 is used as vcc-touchscreen,
config at as such in sun8i-reference-design-tablet.dtsi.

Note that it will only be enabled when it us actually referenced by
a foo-supply property in the touchscreen node, so for tablets which
do not use ldo_io1 as vcc-touchscreen, it will be disabled.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>