dt-bindings: input: iqs269a: Add bindings for slider gestures

This patch adds bindings for slider gestures that can be expressed
by the device.

Signed-off-by: Jeff LaBundy <jeff@labundy.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/ZZMaPrbSi4IrzwKF@nixie71


Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>