libata: Fix several inaccuracies in developer's guide

Commit 6bfff31e (libata: kill probe_ent
and related helpers) killed ata_device_add() but didn't remove references
to it from the libata developer's guide.

Commits 9363c382 (libata: rename SFF
functions) and 5682ed33 (libata: rename
SFF port ops) renamed the taskfile access methods but didn't update the
developer's guide.  Commit c9f75b04
(libata: kill ata_noop_dev_select()) didn't update the developer's
guide as well.

The guide also refers to the long gone ata_pio_data_xfer_noirq(),
ata_pio_data_xfer(), and ata_mmio_data_xfer() -- replace those by
the modern ata_sff_data_xfer_noirq(), ata_sff_data_xfer(), and
ata_sff_data_xfer32().

Also, remove the reference to non-existant ata_port_stop()...

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