webrev for register decoupling changes

[Venkatachalam, Vasanth]

Hi,

Graal's register allocator was previously calling into the x86 runtime to get register numbers to be used for generating HSAIL code.
The x86 register numbers were getting translated into the corresponding HSAIL register mnemonics in the assembler.

This small webrev allows  the register allocator to work with the HSAIL register configuration for getting register numbers to be used for generating HSAIL code.

http://cr.openjdk.java.net/~tdeneau/graal-webrevs/webrev-registerdecoupling/webrev/

Note: HSAIL uses a special calling convention where function params are passed in an arg segment in memory. Currently Graal only supports a choice between a register-based or stack-based calling convention. We have yet to add support for an arg-segment based calling convention. This will be forthcoming in a later patch.  However, the current patch makes the code generation more accurate from the point of view of the HSAIL register configuration.

Please review and provide your feedback.

Vasanth