ide: push end_transfer_func out of start_transfer callback, rename callback

ide: push end_transfer_func out of start_transfer callback, rename callback

Now that end_transfer_func is a tail call in ahci_start_transfer,
formalize the fact that the callback (of which ahci_start_transfer is
the sole implementation) takes care of the transfer too: rename it to
pio_transfer and, if it is present, call the end_transfer_func as soon
as it returns.

Signed-off-by: Paolo Bonzini <[email protected]>
Signed-off-by: John Snow <[email protected]>
Reviewed-by: John Snow <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Message-id: 20180606190955[email protected]
Signed-off-by: John Snow <[email protected]>