Merge pull request #605 from yatharth-arm/yk/sys_counter_fix

Conditionally compile `plat_get_syscnt_freq()` in ARM standard platforms
diff --git a/plat/arm/common/aarch64/arm_common.c b/plat/arm/common/aarch64/arm_common.c
index 74c65ed..cf1f3ba 100644
--- a/plat/arm/common/aarch64/arm_common.c
+++ b/plat/arm/common/aarch64/arm_common.c
@@ -163,6 +163,7 @@
 	return plat_arm_mmap;
 }
 
+#ifdef ARM_SYS_CNTCTL_BASE
 unsigned long long plat_get_syscnt_freq(void)
 {
 	unsigned long long counter_base_frequency;
@@ -176,3 +177,4 @@
 
 	return counter_base_frequency;
 }
+#endif /* ARM_SYS_CNTCTL_BASE */