Request for reviews (XL): 7119644: Increase superword's vector size up to 256 bits

[Vladimir Kozlov]

http://cr.openjdk.java.net/~kvn/7119644/webrev

7119644: Increase superword's vector size up to 256 bits

Increase superword's vector size up to 256-bits for YMM AVX registers on x86. 
Added generation of different vector sizes for different types of arrays in the 
same loop. Allow to generate small (4 bytes) vectors for loops which were 
unrolled small number of iterations.
Add new C2 types for vectors and rework VectorNode implementation. Used 
MachTypeNode as base node for vector mach nodes to keep vector type.
Moved XMM registers definition and vector instructions into one file x86.ad 
(have to rename eRegI to rRegI in x86_32.ad).

Tested with full CTW, NSK, C2 regression tests, JPRT and added new test.

Thanks,
Vladimir