dts: msm8996: replace with upstream DTS

Drop the U-Boot specific dragonboard820c.dts file in favour of the
upstream apq8096-db820c.dts and an additional -u-boot.dtsi with the
U-Boot specific additions.

Taken from kernel tag v6.7

Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Reviewed-by: Sumit Garg <sumit.garg@linaro.org>
Signed-off-by: Caleb Connolly <caleb.connolly@linaro.org>
diff --git a/arch/arm/dts/apq8096-db820c-u-boot.dtsi b/arch/arm/dts/apq8096-db820c-u-boot.dtsi
new file mode 100644
index 0000000..be61ea2
--- /dev/null
+++ b/arch/arm/dts/apq8096-db820c-u-boot.dtsi
@@ -0,0 +1,14 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2024, Linaro Ltd.
+ */
+
+/ {
+	/* Ensure that the fdtfile variable is generated properly */
+	compatible = "qcom,apq8096-db820c", "qcom,apq8096";
+};
+
+&sdhc2 {
+	status = "okay";
+	clock-frequency = <100000000>;
+};