[AsmPrinter] defer %c to base class for ARM, PPC, and Hexagon. NFC

Summary:
None of these derived classes do anything that the base class cannot.
If we remove these case statements, then the base class can handle them
just fine.

Reviewers: peter.smith, echristo

Reviewed By: echristo

Subscribers: nemanjai, javed.absar, eraman, kristof.beyls, hiraditya, kbarton, jsji, llvm-commits, srhines

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D60803

llvm-svn: 358603