[Thumb] 32-bit encodings of 'cps' are not valid for v7M

v7M only allows the 16-bit encoding of the 'cps' (Change Processor
State) instruction, and does not have the 32-bit encoding which is
valid from v6T2 onwards.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218382 91177308-0d34-0410-b5e6-96231b3b80d8