refactor(qemu): do not hardcode counter frequency

From QEMU change:

> In previous versions of the Arm architecture, the frequency of the
> generic timers as reported in CNTFRQ_EL0 could be any IMPDEF value,
> and for QEMU we picked 62.5MHz, giving a timer tick period of 16ns.
> In Armv8.6, the architecture standardized this frequency to 1GHz.

This change stops TF-A from hardcoding 62.5MHz frequency. Instead value
stored in CNTFRQ_EL0 would be used. As a result we get 62.5MHz on older
cores and 1GHz on newer ones.

Change-Id: I7d414ce6d3708e598bbb5a6f79eb2d4ec8e15ac4
Signed-off-by: Marcin Juszkiewicz <marcin.juszkiewicz@linaro.org>
diff --git a/plat/qemu/common/qemu_bl31_setup.c b/plat/qemu/common/qemu_bl31_setup.c
index a627ed7..0a70cc2 100644
--- a/plat/qemu/common/qemu_bl31_setup.c
+++ b/plat/qemu/common/qemu_bl31_setup.c
@@ -161,7 +161,7 @@
 
 unsigned int plat_get_syscnt_freq2(void)
 {
-	return SYS_COUNTER_FREQ_IN_TICKS;
+	return read_cntfrq_el0();
 }
 
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