Sound blaster emulation: When the user specifies sbtype=sb16 when
machine=pcjr or the secondary DMA controller not present, don't force it
to sbtype=sbpro2, print a warning message instead to let the user know
that's a bad idea, but let the user run it that way anyway. Removed
IS_EGAVGA_ARCH check, since the *video card* shouldn't be tied so deeply
to the architecture anyway.