panel: Chain in post-panel-on-command

This is a perfect contended for the `.prepare()` -> `.enable()` split;
on Sony panels the unblank command is typically in `post-panel-on` to
make it happen after the panel is prepared, the bridge is on, and pixel
data is flowing.

Without this pretty much all our panels are generated with a driver that
never unblanks the panel.

Author: MarijnS95

panel.py

@@ -151,6 +151,10 @@ def __init__(self, fdt: Fdt2, node: int, cmd: str) -> None:
 			if init:
 				itr = itertools.chain(init, itr)
 
+			on = fdt.getprop_or_none(node, 'qcom,mdss-dsi-post-panel-on-command')
+			if on:
+				itr = itertools.chain(itr, on)
+
 			on = fdt.getprop_or_none(node, 'lge,display-on-cmds')
 			if on:
 				itr = itertools.chain(itr, on)