ARM: dts: dra7xx: Update spi-max-frequency for QSPI

According to AM572x DM SPRS953A, QSPI max bus speed is 76.8MHz.
Therefore update the spi-max-frequency value of QSPI node for DRA74 and
DRA72 evm. This increase flash read speed by ~2MB/s.

Signed-off-by: Vignesh R <vigneshr@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Jagan Teki <jteki@openedev.com>
Reviewed-by: Mugunthan V N <mugunthanvnm@ti.com>

arch/arm/dts/dra7-evm.dts

@@ -491,7 +491,7 @@
 	pinctrl-names = "default";
 	pinctrl-0 = <&qspi1_pins>;
 
-	spi-max-frequency = <64000000>;
+	spi-max-frequency = <76800000>;
 	m25p80@0 {
 		compatible = "s25fl256s1","spi-flash";
 		spi-max-frequency = <64000000>;

arch/arm/dts/dra72-evm.dts

@@ -603,7 +603,7 @@
 	pinctrl-names = "default";
 	pinctrl-0 = <&qspi1_pins>;
 
-	spi-max-frequency = <64000000>;
+	spi-max-frequency = <76800000>;
 	m25p80@0 {
 		compatible = "s25fl256s1","spi-flash";
 		spi-max-frequency = <64000000>;