[SystemZ] Refactor InstRR* instruction format patterns

This changes the InstRR (and related) patterns to no longer
automatically add an "r" at the end of the mnemonic.  This
makes the .td files more obviously understandable, and also
allows using the patterns for those few instructions that
do not follow the *r scheme.

Also add some more sub-formats of the RRF format class, to
match operand names and sequence from the PoP better.

No functional change.

llvm-svn: 286267