[CodeGen] Print RegClasses on MI in verbose mode

r322086 removed the trailing information describing reg classes for each
register.

This patch adds printing reg classes next to every register when
individual operands/instructions/basic blocks are printed. In the case
of dumping MIR or printing a full function, by default don't print it.

Differential Revision: https://reviews.llvm.org/D42239

llvm-svn: 322867