arm64: dts: ensure backward compatibility of the AP807 Xenon

A recent switch to a dedicated AP807 compatible string for the Xenon
SD/MMC controller result in the driver not being probed when
using updated device tree with the older kernel revisions.
It may also be problematic for other OSs/firmware that use
Linux device tree sources as a reference. Resolve the problem
with backward compatibility by restoring a previous compatible
string as secondary one.
Signed-off-by: Marcin Wojtas <mw@semihalf.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>

arch/arm64/boot/dts/marvell/armada-ap807.dtsi

@@ -29,6 +29,7 @@ cpu_clk: clock-cpu {
 };
 
 &ap_sdhci0 {
-	compatible = "marvell,armada-ap807-sdhci";
+	compatible = "marvell,armada-ap807-sdhci",
+		     "marvell,armada-ap806-sdhci"; /* Backward compatibility */
 };