Request for reviews (S): 8005544: Use 256bit YMM registers in arraycopy stubs on x86

[Vladimir Kozlov]

http://cr.openjdk.java.net/~kvn/8005544/webrev/

New x86 processors with AVX2 have wide memory bus and improved memory 
operations with YMM registers. Use them to copy data in arraycopy stubs.

Most changes in stubGenerator_x86_64.cpp are renaming of copy_32_bytes 
to copy_bytes since now the code copies 64 or 32 bytes per iteration.

Ran compiler regression tests with 64- and 32-bit VM.

Thanks,
Vladimir