isa/sblaster.cpp: convert DSP inner details to a device

[angelosa]

Sound Blaster HLE core currently ties its DSP core to the ISA card. This isn't ideal for both PCI/ISA cards that actually emulates a SB functionality thru a different DSP core (i.e. S3 SonicVibes & SiS 7018), or anything that directly derives the core in the actual Creative Sound Blaster family tree (up to Ensoniq AudioPCI cards?).