[mips] MIPSR6 Compact jump support

This patch adds support for compact jumps similiar to the previous compact
branch support for MIPSR6. Unlike compact branches, compact jumps do not
have a forbidden slot.

As MipsInstrInfo::getEquivalentCompactForm can determine the correct
expansion for jumps and branches for both microMIPS and MIPSR6, remove the
unnecessary distinction in the delay slot filler.

Reviewers: vkalintiris

Subscribers: llvm-commits, dsanders
llvm-svn: 265390