Some controllers (jmb and inic162x) use 0x77 and 0x7f to indicate that
the device isn't ready yet.  It looks like they use 0xff if device
presence is detected but connection isn't established.  0x77 or 0x7f
after connection is established and use the value from signature FIS
after receiving it.

This patch implements ata_check_ready(), which takes TF status value
and determines whether the port is ready or not considering the above
and other conditions, and use it in @check_ready() functions.  This is
safe as both 0x77 and 0x7f aren't valid ready status value even though
they have BSY bit cleared.

This fixes hot plug detection failures which can be triggered with
certain drives if they aren't already spun up when the data connector
is hot plugged.

Tested on sil, sil24, ahci (jmb/ich), piix and inic162x combined with
eight drives from all major vendors.
Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>