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.

driver.py

@@ -136,6 +136,9 @@ def generate_commands(p: Panel, options: Options, cmd_name: str) -> str:
 			s += '\n'
 		block = '{' in c.generated
 
+		if cmd_name == 'on' and 'panel_power_on' in cmd.generated:
+			s += '/* FIXME: Call this in .enable() */\n'
+
 		s += c.generated + '\n'
 		if c.wait and c.wait > options.ignore_wait:
 			s += f'\t{msleep(c.wait)};\n'

panel.py

@@ -156,6 +156,10 @@ 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)