libvecpf: Missing VSX cleanup in Makefile

This patch removes the VSX rules to defines or not TEST_VSX
when building the tests (which is not required anymore).
libvecpf: Fix vector_mods register and build on LE

This patch fixes a wrong vector_mods setup (due recent patches) and also
adds -Wl,--no-as-needed to avoid erros on system that enables -Wl,--as-needed
as default (Ubuntu).