[documentation][llvm-mca] Update the documentation.

Scheduling models can now describe processor register files and retire control
units. This updates the existing documentation and the README file.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@329311 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed