mips64: add cases in wrappers for ptrace calls with GETREGSET

Add cases for PTRACE_GETREGSET in PRE(sys_ptrace) and POST(sys_ptrace).

This fixes memcheck/tests/linux/getregset on MIPS64 platforms with kernel
that supports ptrace call with PTRACE_GETREGSET.


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13418 a5019735-40e9-0310-863c-91ae7b9d1cf9