ide_pci_setup_ports() from setup-pci.c checks if port is disabled, if so
d->init_setup_dma() and d->init_hwif() won't be called.  There is no need
to check it once again inside init_hwif_amd74xx(), init_dma_amd74xx()
and amd74xx_tune_drive() (hwif->tuneproc will be NULL for disabled port).

Therefore remove amd_enabled variable and now unnecessary init_dma_amd74xx().
Also do not set .init_{iops, dma} to NULL in amd74xx.h (amd74xx_chipsets[]
is declared static).  Bump driver's version number to reflect changes.

Almost identical to the previous VIA case.