perf, MIPS: Support cross compiling of tools/perf for MIPS

Changes:
 v4: Fix the cosmetic issue of redundant dot-ops
 v3: Change rmb() to use SYNC
 v2: Include mips unistd.h and define rmb()/cpu_relax() in tools/perf/perf.h
Signed-off-by: NDeng-Cheng Zhu <dengcheng.zhu@gmail.com>
Acked-by: NRalf Baechle <ralf@linux-mips.org>
Cc: David Daney <ddaney@caviumnetworks.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

tools/perf/perf.h

@@ -73,6 +73,18 @@ void get_term_dimensions(struct winsize *ws);
 #define cpu_relax()	asm volatile("":::"memory")
 #endif
 
+#ifdef __mips__
+#include "../../arch/mips/include/asm/unistd.h"
+#define rmb()		asm volatile(					\
+				".set	mips2\n\t"			\
+				"sync\n\t"				\
+				".set	mips0"				\
+				: /* no output */			\
+				: /* no input */			\
+				: "memory")
+#define cpu_relax()	asm volatile("" ::: "memory")
+#endif
+
 #include <time.h>
 #include <unistd.h>
 #include <sys/types.h>