[CodeGenSchedule][NFC] Always emit ProcResourceUnits.

Summary:
Right now only the ProcResourceUnits that are directly referenced by
instructions are emitted. This change emits all of them, so that
analysis passes can use the information.
This has no functional impact. It typically adds a few entries (e.g. 4
for X86/haswell) to the generated ProcRes table.

Reviewers: gchatelet

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D42903

llvm-svn: 324228