aarch64/styx-dcp-sc-28p-a: Fix warm reset on old rev. a boards

Rev. A has a FLASH that Linux reconfigures to 4B-addressing, but must
be in 3B-addressing when accessed by the BootROM. Since it has no
reset input, this would not work on warm resets. Linux has a
workaround for this issue for the common case of a controlled reboot,
which this change enables on those boards (which are admittedly few
and far between, but still useful as testing vehicles).

(This won't take effect until Finit is updated to at least 4.15, which
switches over from watchdog- to reboot(2)- based reboot, by default)

board/aarch64/styx-dcp-sc-28p/dts/styx/dcp-sc-28p-a.dts

@@ -59,3 +59,9 @@
 		XSWP(a, "e13", 13, &sfp0);
 	};
 };
+
+&cp0_spi1 {
+	spi-flash@0 {
+		broken-flash-reset;
+	};
+};