perf tools: Fix arm64 build error

I'm seeing the following build error on arm64:

  In file included from util/event.c:3:0:
  util/event.h:95:17: error: 'PERF_REGS_MAX' undeclared here (not in a function)
    u64 cache_regs[PERF_REGS_MAX];
                 ^

This patch adds a PERF_REGS_MAX definition for arm64.
Signed-off-by: Mark Salter <msalter@redhat.com>
Acked-by: Jean Pihet <jean.pihet@linaro.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jean Pihet <jean.pihet@linaro.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1406325766-8085-1-git-send-email-msalter@redhat.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/arch/arm64/include/perf_regs.h

@@ -6,6 +6,8 @@
 #include <asm/perf_regs.h>
 
 #define PERF_REGS_MASK	((1ULL << PERF_REG_ARM64_MAX) - 1)
+#define PERF_REGS_MAX	PERF_REG_ARM64_MAX
+
 #define PERF_REG_IP	PERF_REG_ARM64_PC
 #define PERF_REG_SP	PERF_REG_ARM64_SP