EBUS DMA fixes:
- Add EBUS_DMA_FLAG_TCI_DISABLE that the client can set if it
  wants only to hear device interrupts, not DMA complete ones.
- When initially resetting the EBUS DMA unit, put valid burst etc.
  encodings in the CSR register.  Not doing this appears to leave
  the attached ISA device in a weird state.

PCI FLOPPY fixes:
- Do ebus_dma_enable() before ebus_dma_request()
- In sun_pci_fd_set_dma_mode() do not forget to set the direction.
- Set EBUS_DMA_FLAG_TCI_DISABLE in ebus_dma flags.
- Make sure that in error paths sun_fdc/FCD1 will be -1 (invalid).

Thanks to Soyoung Park for loaning her Ultra5 to me so I could fix this.