Bug 323893 - SSE3 not available on amd cpus in valgrind.

Check minimum hardware capabilities, not exact matches to prevent
downgrading to baseline if the hardware has more capabilities than
we expect.

Note that this is still not exactly correct. CPUID should depend on
VEX capabilities, not on underlying CPU, see bug 324882.

git-svn-id: svn://svn.valgrind.org/vex/trunk@2761 8f6e269a-dfd6-0310-a8e1-e2731360e62c