[llvm-exegesis] Add AArch64 operand initializers, SetRegTo (#169912)
Make llvm-exegesis more usable on AArch64 by doing the following:
Add some missing exegesis handling of register classes;
Add some missing LLVM AArch64 OperandTypes.
Llvm-exegesis can now handle many more AArch64 instructions.
AArch64 load/store instructions are not yet supported by llvm-exegesis,
until https://github.com/llvm/llvm-project/pull/144895 lands.
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Co-authored-by: Cullen Rhodes <cullen.rhodes@arm.com>