[mips][msa] Rename main check prefix to 'ALL' in basic operations tests. NFC

Summary:
The majority of the checks are subtarget independent. The few that aren't
will be corrected shortly.

Reviewers: vkalintiris

Reviewed By: vkalintiris

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D9340

llvm-svn: 236220