MIPS64: Fix ExternalCallbackScope() to adapt 64-bit simulator.

Fixed in r19311/75295c56

TEST: cctest/test-cpu-profiler/NativeAccessorUninitializedIC (only fix on sim)
      cctest/test-cpu-profiler/NativeAccessorMonomorphicIC (only fix on sim)
      cctest/test-cpu-profiler/NativeMethodMonomorphicIC (only fix on sim)
MIPS64: Fix abi issues in Deoptimizer::EntryGenerator
Merge remote-tracking branch 'mrb/yy-dev-mips64-2' into pldev-05