Input: sun4i-a10-lradc-keys - add support for A83T

Allwinner A83T SoC has a low res adc like the one in Allwinner A10 SoC,
however, the A10 SoC's vref of lradc internally is divided by 2/3 and
the A83T SoC's vref of lradc internally is divided by 3/4, thus add
a hardware variant for it to be compatible with various devices.

Signed-off-by: Ziping Chen <techping.chan@gmail.com>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>