dt-bindings: pwm: opencores: Add compatible for StarFive JH8100

StarFive JH8100 uses the same OpenCores PWM controller as JH7110.
Mark JH8100 as compatible to the OpenCores PWM controller.

Signed-off-by: Ley Foon Tan <leyfoon.tan@starfivetech.com>
Signed-off-by: Ji Sheng Teoh <jisheng.teoh@starfivetech.com>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>