[mips] Expand JAL instructions when PIC is enabled.

Summary: This is the correct way to handle JAL instructions when PIC is enabled.

Patch by Toma Tabacu

Reviewers: seanbruno, tomatabacu

Subscribers: brooks, seanbruno, emaste, llvm-commits

Differential Revision: http://reviews.llvm.org/D6231

llvm-svn: 245305