arm64: dts: rockchip: Add enable-strobe-pulldown to emmc phy on ROCK 4C+

Commit 8b5c2b45 disabled the internal pull-down for the strobe line
causing I/O errors in HS400 mode for various eMMC modules.

Enable the internal strobe pull-down for the ROCK 4C+ board. Also re-enable
HS400 mode, that was replaced with HS200 mode as a workaround for the
stability issues in:
2bd1d2dd ("arm64: dts: rockchip: Disable HS400 for eMMC on ROCK 4C+").

Fixes: 8b5c2b45 ("phy: rockchip: set pulldown for strobe line in dts")
Signed-off-by: Folker Schwesinger <dev@folker-schwesinger.de>
Reviewed-by: Dragan Simic <dsimic@manjaro.org>
Link: https://lore.kernel.org/r/20240327192641.14220-3-dev@folker-schwesinger.deSigned-off-by: Heiko Stuebner <heiko@sntech.de>

arch/arm64/boot/dts/rockchip/rk3399-rock-4c-plus.dts

@@ -151,6 +151,7 @@ &cpu_b1 {
 };
 
 &emmc_phy {
+	rockchip,enable-strobe-pulldown;
 	status = "okay";
 };
 
@@ -549,7 +550,8 @@ &saradc {
 &sdhci {
 	max-frequency = <150000000>;
 	bus-width = <8>;
-	mmc-hs200-1_8v;
+	mmc-hs400-1_8v;
+	mmc-hs400-enhanced-strobe;
 	non-removable;
 	status = "okay";
 };