mips64: add missing headers to EXTRA_DIST

make dist will not copy header files if they are not explicitly listed
in EXTRA_DIST. This change adds missing header files from none/test/mips64.


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13701 a5019735-40e9-0310-863c-91ae7b9d1cf9