armv8/ls2085a: Fix generic timer clock source

The timer clock is system clock divided by 4, not fixed 12MHz.
This is common to the SoC, not board specific. Primary core is
fixed when u-boot still runs in board_f. Secondary cores are
fixed by reading a variable set by u-boot.

Signed-off-by: York Sun <yorksun@freescale.com>
CC: Mark Rutland <mark.rutland@arm.com>

README

@@ -690,6 +690,14 @@ The following options need to be configured:
 		exists, unlike the similar options in the Linux kernel. Do not
 		set these options unless they apply!
 
+		COUNTER_FREQUENCY
+		Generic timer clock source frequency.
+
+		COUNTER_FREQUENCY_REAL
+		Generic timer clock source frequency if the real clock is
+		different from COUNTER_FREQUENCY, and can only be determined
+		at run time.
+
 		NOTE: The following can be machine specific errata. These
 		do have ability to provide rudimentary version and machine
 		specific checks, but expect no product checks.