Replace ValueTypes.h with MachineValueType.h if possible.

Utilize the previous move of MVT to a separate header for all trivial
cases (that don't need any further restructuring).

Reviewed By: Tim Northover

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204003 91177308-0d34-0410-b5e6-96231b3b80d8