Move mips1 tests to test/MC/Disassembler/Mips/mips1

This matches the pattern of the mips2 and 3 tests, as well as our normal
conventions.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224254 91177308-0d34-0410-b5e6-96231b3b80d8