Apparently, the "regType" and "regClass" used in the Sparc backend are not both

Apparently, the "regType" and "regClass" used in the Sparc backend are not both
correct: empirically, "regType" is wrong for a number of registers. Thus, one
can only rely on the "regClass" to figure out what kind of register one is
dealing with.

This change switches to using only "regClass" and adds a few extra DEBUG() print
statements and a few clean-ups in comments and code, mostly minor.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@7103 91177308-0d34-0410-b5e6-96231b3b80d8