arm: vexpress64: Fix counter frequency

The arch timer on 64-bit Arm Ltd. platforms is driven by a 24 MHz
crystal oscillator, so the frequency is not 25165824 MHz, as the current
code suggests.
Signed-off-by: NAndre Przywara <andre.przywara@arm.com>
Reviewed-by: NLinus Walleij <linus.walleij@linaro.org>

include/configs/vexpress_aemv8a.h

@@ -68,7 +68,7 @@
 #define V2M_SYS_CFGSTAT			(V2M_SYSREGS + 0x0a8)
 
 /* Generic Timer Definitions */
-#define COUNTER_FREQUENCY		(0x1800000)	/* 24MHz */
+#define COUNTER_FREQUENCY		24000000	/* 24MHz */
 
 /* Generic Interrupt Controller Definitions */
 #ifdef CONFIG_GICV3