Replaces ArchDefault method with Crankshaft and Turbofan getters.
Eliminates IsAllocated method on Register, FloatRegister, DoubleRegister.
Eliminates ToString method too.
Changes call sites to access appropriate arch default RegisterConfiguration.

LOG=N
BUG=

Review-Url: https://codereview.chromium.org/2092413002
Cr-Commit-Position: refs/heads/master@{#37297}