[ARM] Pass for Cortex-A57 and Cortex-A72 Fused AES Erratum

[ARM] Pass for Cortex-A57 and Cortex-A72 Fused AES Erratum

This adds a late Machine Pass to work around a Cortex CPU Erratum
affecting Cortex-A57 and Cortex-A72:
- Cortex-A57 Erratum 1742098
- Cortex-A72 Erratum 1655431

The pass inserts instructions to make the inputs to the fused AES
instruction pairs no longer trigger the erratum. Here the pass errs on
the side of caution, inserting the instructions wherever we cannot prove
that the inputs came from a safe instruction.

The pass is used:
- for Cortex-A57 and Cortex-A72,
- for "generic" cores (which are used when using `-march=`),
- when the user specifies `-mfix-cortex-a57-aes-1742098` or
  `mfix-cortex-a72-aes-1655431` in the command-line arguments to clang.

Reviewed By: dmgreen, simon_tatham

Differential Revision: https://reviews.llvm.org/D119720