lib/cobalt/arm64: dovetail: skip detection of KUSER_TSC support

When Dovetail is enabled in the kernel, we get timestamps for common
clocks (CLOCK_REALTIME, CLOCK_MONOTONIC) from the vDSO-based gettime()
routine as usual.  Do not expect KUSER_TSC support to be there in such
a case, it is not.
Signed-off-by: Philippe Gerum <rpm@xenomai.org>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

lib/cobalt/arch/arm64/features.c

@@ -25,6 +25,7 @@
 #include <unistd.h>
 #include <limits.h>
 #include <cobalt/wrappers.h>
+#include <cobalt/ticks.h>
 #include <asm/xenomai/syscall.h>
 #include <asm/xenomai/tsc.h>
 #include <asm/xenomai/features.h>
@@ -44,6 +45,9 @@ void cobalt_arch_check_features(struct cobalt_featinfo *finfo)
 	int err, fd;
 	void *addr;
 
+	if (!cobalt_use_legacy_tsc())
+		return;
+
 	if (__xn_tscinfo.kinfo.counter != NULL)
 		return;