armv8: configs: ls1012a: correct the generic timer frequency

On ls1012a soc, core clock source frequency is fixed at 100Mhz.
Generic timer frequency is core clock source divided by 4, which
is 25Mhz.

Signed-off-by: Tang Yuantian <andy.tang@nxp.com>
Reviewed-by: York Sun <york.sun@nxp.com>

include/configs/ls1012a_common.h

@@ -32,7 +32,7 @@
 #define CONFIG_SYS_DDR_BLOCK2_BASE     0x880000000ULL
 
 /* Generic Timer Definitions */
-#define COUNTER_FREQUENCY		CONFIG_SYS_CLK_FREQ/4	/* 25MHz */
+#define COUNTER_FREQUENCY		25000000	/* 25MHz */
 
 /* CSU */
 #define CONFIG_LAYERSCAPE_NS_ACCESS