dt-bindings: pwm: Convert BCM7038 PWM binding to YAML

Convert the Broadcom STB BCM7038 PWM Device Tree binding to YAML to help
with validation.

Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20211208003727.3596577-4-f.fainelli@gmail.com


Signed-off-by: Rob Herring <robh@kernel.org>