pwm: jz4740: Add support for devicetree

Add support for probing the pwm-jz4740 directly from devicetree.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>