Function 3     : Initialize Driver.

Entry          : BX = 3.
Exit           : AX = 0, Succesfully initialize.
                      1, Voice card fails.
                      2, I/O read / write fails.
                      3, Interrupt for DMA, fails.

If the default I/O Address or interrupt needs to be
changed, "Set Base I/O Address" and "Set interrupt Number"
have to be called before invoking this function.

This function checks for the correct setting and the funtionality
of the Sound Blaster Card. If the Sound Blaster Card is initialised
succesfully, it will return a 0 in AX.

Otherwise, an error with a non-zero value is returned. The calling
program should abort when an error occurrs.

The DAC connection to the speaker is turned on after the card has been
initialized.

Except the functions 0- 2, all other driver fumctions can only be called after
this function has being invoked. This function only needs to be called once.