ARM: dts: ls1021a-tsn: use generic "jedec,spi-nor" compatible for flash

We cannot list all the possible chips used in different board revisions,
just use the generic "jedec,spi-nor" compatible instead.  This also
fixes dtbs_check error:
['jedec,spi-nor', 's25fl256s1', 's25fl512s'] is too long
Signed-off-by: Li Yang <leoyang.li@nxp.com>
Reviewed-by: Kuldeep Singh <kuldeep.singh@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/ls1021a-tsn.dts

@@ -251,7 +251,7 @@ &qspi {
 
 	flash@0 {
 		/* Rev. A uses 64MB flash, Rev. B & C use 32MB flash */
-		compatible = "jedec,spi-nor", "s25fl256s1", "s25fl512s";
+		compatible = "jedec,spi-nor";
 		spi-max-frequency = <20000000>;
 		#address-cells = <1>;
 		#size-cells = <1>;