[mips] Generate code for insert/extract operations when using the N64 ABI and MSA.

Summary:
When using the N64 ABI, element-indices use the i64 type instead of i32.
In many cases, we can use iPTR to account for this but additional patterns
and pseudo's are also required.

This fixes most (but not quite all) failures in the test-suite when using
N64 and MSA together.

Reviewers: vkalintiris

Reviewed By: vkalintiris

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D9342

llvm-svn: 236494