arm64: dts: rockchip: Add missing sdmmc2 SDR rates to rock-3a

Add missing UHS-I SDR rates to sdmmc2. Add explicit alias as mmc2 while at it.
It would be good to have matching timings enabled in case slower SDIO devices
are encountered.
Signed-off-by: Tamás Szűcs <tszucs@protonmail.ch>
Link: https://lore.kernel.org/r/20231011191448.58936-1-tszucs@protonmail.chSigned-off-by: Heiko Stuebner <heiko@sntech.de>

arch/arm64/boot/dts/rockchip/rk3568-rock-3a.dts

@@ -15,6 +15,7 @@ aliases {
 		ethernet0 = &gmac1;
 		mmc0 = &sdhci;
 		mmc1 = &sdmmc0;
+		mmc2 = &sdmmc2;
 	};
 
 	chosen: chosen {
@@ -747,6 +748,9 @@ &sdmmc2 {
 	non-removable;
 	pinctrl-names = "default";
 	pinctrl-0 = <&sdmmc2m0_bus4 &sdmmc2m0_cmd &sdmmc2m0_clk>;
+	sd-uhs-sdr12;
+	sd-uhs-sdr25;
+	sd-uhs-sdr50;
 	sd-uhs-sdr104;
 	vmmc-supply = <&vcc3v3_sys>;
 	vqmmc-supply = <&vcc_1v8>;