MIPS: Eliminate code duplication in lithium calls to vector-based LoadICs.

Port r23359 (2e682e9)

BUG=
R=paul.lind@imgtec.com

Review URL: https://codereview.chromium.org/503103002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23372 ce2b1a6d-e550-0410-aec6-3dcde31c8c00