Restore CodeGen/MachineValueType.h from `Support`

This is rework of;

  - rG13e77db2df94 (r328395; MVT)

Since `LowLevelType.h` has been restored to `CodeGen`, `MachinveValueType.h`
can be restored as well.

Depends on d1487670

Differential Revision: https://reviews.llvm.org/D149024