Added Subtarget support into RegisterInfo

Added HasABICall and HasAbsoluteCall (equivalent to gcc -mabicall and 
-mno-shared). HasAbsoluteCall is not implemented but HasABICall is the 
default for o32 ABI. Now, both should help into a more accurate 
relocation types implementation. 
Added IsLinux is needed to choose between asm directives.
Instruction name strings cleanup.
AsmPrinter improved.

llvm-svn: 53551