[X86] Add some instruction aliases to get the assembly parser table to favor arithmet...

[X86] Add some instruction aliases to get the assembly parser table to favor arithmetic instructions with 8-bit immediates over the forms that implicitly use the ax/eax/rax.

This allows us to remove the explicit code for working around the existing priority

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@250011 91177308-0d34-0410-b5e6-96231b3b80d8