Eliminated the classification of control registers into %ecr_

Eliminated the classification of control registers into %ecr_
and %rcr_, leaving just %cr_ which is what people expect.
Updated the disassembler to support this unified register set.
Added a testcase to verify that the registers continue to be
decoded correctly.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@103196 91177308-0d34-0410-b5e6-96231b3b80d8