pata_cmd64x: turn string of *if* statements into *switch*

Convert string of the *if* statements all checking 'pdev->revision' into more
natural *switch* statement. While at it, somewhat clarify the comments there...

Increment the driver version, accounting for the patches that neglected to do
this in the past.

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>