dt-bindings: sc16is7xx: Add flag to activate IrDA mode

This series of uart controllers is able to work in IrDA mode.
This adds a property to the device tree to enable that feature on
selected ports if needed.

Signed-off-by: Pascal Huerst <pascal.huerst@gmail.com>
Signed-off-by: Daniel Mack <daniel@zonque.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20200529055058.1606910-2-daniel@zonque.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>