arm64: dts: qcom: sc7280: Power herobrine's 3.3 eDP/TS rail more properly

This is the equivalent of commit f5b4811e ("arm64: dts: qcom:
sc7180: Add trogdor eDP/touchscreen regulator off-on-time") and commit
23ff8669 ("arm64: dts: qcom: sc7180: Start the trogdor
eDP/touchscreen regulator on"), but for herobrine instead of trogdor.

The motivations for herobrine are the same as for trogdor.

NOTES:
* Currently for herobrine all boards are eDP, not MIPI. If/when we
  have herobrine derivatives that are MIPI they we can evaluate
  whether the same off-on-delay makes sense for them. For trogdor we
  didn't add the delay to MIPI panels because the problem was found
  late and nobody had complained about it. For herobrine defaulting to
  assuming the same 500ms makes sense and if we find we need to
  optimize later we can.
* Currently there are no oddball herobrine boards like homestar where
  the panel really likes to be power cycled. If we have an oddball
  board it will need to split the eDP and touchscreen rail anyway
  (like homestar did) and we'll have to delete the "regulator-boot-on"
  from that board.
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230207163550.1.I5ff72b7746d5fca8f10ea61351bde4150ed1a7f8@changeid

arch/arm64/boot/dts/qcom/sc7280-herobrine.dtsi

@@ -110,6 +110,22 @@ pp3300_left_in_mlb: pp3300-left-in-mlb-regulator {
 
 		regulator-enable-ramp-delay = <3000>;
 
+		/*
+		 * eDP panel specs nearly always have a spec that says you
+		 * shouldn't turn them off an on again without waiting 500ms.
+		 * Add this as a board constraint since this rail is shared
+		 * between the panel and touchscreen.
+		 */
+		off-on-delay-us = <500000>;
+
+		/*
+		 * Stat the regulator on. This has the advantage of starting
+		 * the slow process of powering the panel on as soon as we
+		 * probe the regulator. It also avoids tripping the
+		 * off-on-delay immediately on every bootup.
+		 */
+		regulator-boot-on;
+
 		vin-supply = <&pp3300_z1>;
 	};