implement timer for arm >= v6

Signed-off-by: Khem Raj <raj.khem@gmail.com>
--- a/utilities/transactions/lock/range/range_tree/lib/portability/toku_time.h
+++ b/utilities/transactions/lock/range/range_tree/lib/portability/toku_time.h
@@ -161,6 +161,20 @@ static inline tokutime_t toku_time_now(v
   struct timeval tv;
   gettimeofday(&tv, nullptr);
   return (uint64_t)tv.tv_sec * 1000000 + tv.tv_usec;
+#elif (__ARM_ARCH >= 6)
+  uint32_t pmccntr;
+  uint32_t pmuseren;
+  uint32_t pmcntenset;
+  // Read the user mode perf monitor counter access permissions.
+  asm volatile("mrc p15, 0, %0, c9, c14, 0" : "=r"(pmuseren));
+  if (pmuseren & 1) {  // Allows reading perfmon counters for user mode code.
+    asm volatile("mrc p15, 0, %0, c9, c12, 1" : "=r"(pmcntenset));
+    if (pmcntenset & 0x80000000ul) {  // Is it counting?
+      asm volatile("mrc p15, 0, %0, c9, c13, 0" : "=r"(pmccntr));
+      // The counter is set up to count every 64th cycle
+      return (uint64_t)pmccntr * 64;  // Should optimize to << 6
+    }
+  }
 #else
 #error No timer implementation for this platform
 #endif