dt-bindings: devfreq: event: rockchip,dfi: Add rk3568 support

dt-bindings: devfreq: event: rockchip,dfi: Add rk3568 support

This adds the rockchip,rk3568-dfi compatible to the binding. Make clocks
optional for this SoC as the RK3568 doesn't have a kernel controllable
PCLK.

Link: https://lore.kernel.org/all/20231018061714.3553817-22-s.hauer@pengutronix.de/
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Acked-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>