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: Deng-Cheng Zhu <[e-mail]>
Acked-by: Ralf Baechle <[e-mail]>
Cc: David Daney <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Arnaldo Carvalho de Melo <[e-mail]>
Cc: Frederic Weisbecker <[e-mail]>
Cc: Paul Mackerras <[e-mail]>
Signed-off-by: Ingo Molnar <[e-mail]>

tools/perf/perf.h

···
 #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>