[ARM64] Simplify RegisterInfos_arm64.h with macro based RegisterInfo array
This patches paves way for upcoming SVE RegisterInfo definitions. This is cosmetic change which allows us to define ARM64 RegisterInfo using macros.
In future we ll have define two different RegisterInfos to choose between SVE vs non-SVE RegisterInfo with decision being made at thread creation.
Differential Revision: https://reviews.llvm.org/D66934