ath79: enable m25p,fast-read for tplink,tl-wr2543-v1

Enables spi-mem interface usage. It speeds up flash read
in about 3x while it also workaround a possible hardware
bug when normal spi read is used.

Fixes: FS#2742

Signed-off-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>

target/linux/ath79/dts/ar7242_tplink_tl-wr2543-v1.dts

@@ -109,6 +109,7 @@
 		compatible = "jedec,spi-nor";
 		reg = <0>;
 		spi-max-frequency = <25000000>;
+		m25p,fast-read;
 
 		partitions {
 			compatible = "fixed-partitions";