[15] RFR (S): x86: Remove MMX support

[Vladimir Ivanov]

http://cr.openjdk.java.net/~vlivanov/8241597/webrev.00/
https://bugs.openjdk.java.net/browse/JDK-8241597

MMX is not used in x86-64 code.

Instead of making relevant code 32-bit only, I propose to remove all 
usages from both x86-64 and x86-32 specific code. (The only piece left 
is Assembler::emms() which is used in MacroAssembler::empty_FPU_stack().)

Also, got rid of VM_Version::supports_mmx_ext() along the way.

Testing: hs-tier1,hs-tier2, successfully built x86-32 (just a build, no 
additional testing performed)

Thanks!

Best regards,
Vladimir Ivanov