Makes the use of the interface a little less noisy, especially given
how much of the interface depends on an instance being present.

Given how many member functions make use of the system instance,
it's likely just better to pass the system instance in on construction.

Makes the interface a little less noisy to use.

VideoCommon: Reword the unknown opcode error message

When faced with this error, users often don't try disabling dual core,
even though the error message suggests it. Perhaps the message is just
too long and lists too many things?

To try to improve the situation, I'm rewording the message and making it
say different things depending on what settings you are using.