panel: Chain on command from post-on-backlight

Someone linked this:
https://github.com/Saikatsaha1996/android_kernel_oneplus_sm8350/blob/9c86b0cf0172c8ca42ed377af48c0e877ba7a050/arch/arm64/boot/dts/vendor/oplus/porsche/dsi-panel-oplus21617-samsung-ams662zs01-1080-2400-dvt-dsc-cmd.dtsi#L158-L161

And their generated panel indeed never unblanks at the end of _on():
https://github.com/Saikatsaha1996/linux-sm8350/blob/b7975f1ae5fd4aa9eac89b2777df0d72ba3e2082/drivers/gpu/drm/panel/panel-samsung-ams662zs01.c#L108

panel.py

@@ -160,6 +160,10 @@ def __init__(self, fdt: Fdt2, node: int, cmd: str) -> None:
 			if on:
 				itr = itertools.chain(itr, on)
 
+			on = fdt.getprop_or_none(node, 'qcom,mdss-dsi-post-on-backlight')
+			if on:
+				itr = itertools.chain(itr, on)
+
 			on = fdt.getprop_or_none(node, 'lge,display-on-cmds')
 			if on:
 				itr = itertools.chain(itr, on)