dt-bindings: connector: Add support for USB-PD PPS APDOs to bindings

Add support for PPS APDOs to connector bindings so a port controller
can specify support for PPS, as per existing FIXED/BATT/VAR PDOs.

Signed-off-by: Adam Thomson <Adam.Thomson.Opensource@diasemi.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>