perf: Enable building perf tools for Meta

Define rmb(), cpu_relax(), and CPUINFO_PROC for Meta so that the perf
tools can be built for Meta.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>

tools/perf/perf.h

@@ -98,6 +98,12 @@ void get_term_dimensions(struct winsize *ws);
 #define CPUINFO_PROC	"cpu model"
 #endif
 
+#ifdef __metag__
+#define rmb()		asm volatile("" ::: "memory")
+#define cpu_relax()	asm volatile("" ::: "memory")
+#define CPUINFO_PROC	"CPU"
+#endif
+
 #include <time.h>
 #include <unistd.h>
 #include <sys/types.h>