[llvm-mca][docs] Move the code marker text into its own subsection. NFC.

Also fixed a few undecorated 'llvm-mca' references to be highlighted
with the 'program' emphasis.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@338900 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed