Utilization of non-original code within Espruino?

Well, if you absolutely had to I would contact the author and see if he'd be happy for it to use the MPLv2 license (he probably would be), then you can include it under MPLv2.

BUT the library is just a collection of register poking code that's also available elsewhere it seems (if you google bits of it). That code should really go in jshardware.c, not a separate library - especially as the library would need quite a lot of modification to work efficiently with Espruino's jsSPISend command. You're basically going to end up rewriting it anyway.