Inline assembler: partly added constraints support.
Refactored GPR8 registers class, added new registers classes: lGPR8, hGPR8, simplehGPR8 and specialUpperGPR8.
Inline asm: Finished (not tested yet) constraints implementation.
Fixed register size for specialUpperGPR8.
Tests for inline assembler registers constraints.
TODO: For proper non-registers contraint implementation we need to implement TargetLowering::LowerAsmOperandForConstraint hook.