GlobalISel: Translate ConstantDataVector

Reviewers: qcolombet, aditya_nandakumar, dsanders, t.p.northover, javed.absar, ab

Reviewed By: qcolombet, dsanders, ab

Subscribers: dberris, rovka, llvm-commits, kristof.beyls

Differential Revision: https://reviews.llvm.org/D30216

llvm-svn: 297670