[TableGen][SubtargetEmitter] Refactor hasReadOfWrite to CodeGenProcModel (#92032)

SubtargetEmitter::GenSchedClassTables takes a CodeGenProcModel, but
calls hasReadOfWrite which loops over all ProcModels. We move
hasReadOfWrite to CodeGenProcModel and remove the loop over all
ProcModels. This leads to a 144% speedup on the RISC-V backend of our
downstream.