[mips] Fix machine verifier errors in the long branch pass

This patch fixes two systemic machine verifier errors in the long
branch pass. The first is the incorrect basic block successors
and the second was the incorrect construction of several jump
instructions.

This partially resolves PR27458 and the associated PR32146.

Reviewers: slthakur

Differential Revision: https://reviews.llvm.org/D33378

llvm-svn: 305382