Add a third (and optional) parameter to microcode selection filters, to
select microcodes by revision.  The revision can be prefixed by the
operators eq: (equal to), lt: (less than), or gt: (greater than).

The revision numbering is signed, but in order to be more user friendly,
since we display revisions as unsigned values in hex, we accept the
range -INT32_MAX to +UINT32_MAX, and convert it to int32_t.