pwm: Add PWM polarity flag macro for DT

Define a PWM_POLARITY_INVERTED macro in include/dt-bindings/pwm/pwm.h to
be used by device tree sources.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

diff --cc Documentation/devicetree/bindings/pwm/pwm.txt
Simple merge

diff --cc include/dt-bindings/pwm/pwm.h
Simple merge