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/Makefile b/arch/arm/dts/Makefile
index adb03a5..992ae25 100644
--- a/arch/arm/dts/Makefile
+++ b/arch/arm/dts/Makefile
@@ -625,7 +625,7 @@
 dtb-$(CONFIG_TARGET_TEN64) += fsl-ls1088a-ten64.dtb
 
 dtb-$(CONFIG_ARCH_SNAPDRAGON) += apq8016-sbc.dtb \
-	dragonboard820c.dtb \
+	apq8096-db820c.dtb \
 	sdm845-db845c.dtb \
 	sdm845-samsung-starqltechn.dtb \
 	qcs404-evb.dtb