mips64: add tests for load indexed instructions

Tests that should be executed on MIPS64 platforms that support lwx, ldx
and lbux.

Relevant VEX change - r2819.

Patch by Zahid Anwar, with some changes.

Related to Bugzilla issue 326444. It closes this issue now.


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13808 a5019735-40e9-0310-863c-91ae7b9d1cf9