[mips] Move MC tests for the DSP ASE into the standard format.

Summary:
Only DSPr2 is present because it appears we've never added DSPr1 tests.
We'll have to correct that in a later patch.

Reviewers: vkalintiris

Subscribers: llvm-commits, dsanders

Differential Revision: http://reviews.llvm.org/D14448

llvm-svn: 252752