[llvm-mc] Add -M to replace -riscv-no-aliases and -riscv-arch-reg-names
In objdump, many targets support -M no-aliases. Instead of having a
-*-no-aliases for each target when LLVM adds the support, it makes more sense
to introduce objdump style -M.
-riscv-arch-reg-names is removed. -riscv-no-aliases has too many uses and thus is retained for now.
Reviewed By: luismarques
Differential Revision: https://reviews.llvm.org/D103004