sata_nv: use hardreset only for post-boot probing

When I thought it was finally defeated, it came back with vengeance.
The failure cases are ever more convoluted.  Now there is a single
combination which fails boot probing - MCP5x + Intel SSD and there are
two hotplug failure reports on different flavors where softreset fails
to bring up the device.

Through the many bug reports after the switch to hardreset, the
following patterns emerged.

- Softreset during boot always works.

- Hardreset during boot sometimes fails to bring up the link on
  certain comibnations and device signature acquisition is unreliable.

- Hardreset is often necessary after hotplug.

It looks like the old behavior of preferring softreset was somehow
pretty close to the working reset protocol although it could have lost
a device during phy error handling by issuing hardreset.

This patch implements nv_hardreset() which kicks in only for post-boot
(!LOADING) device probing resets.  This should be able to work around
all known problem cases.  This isn't perfect but given the various
hardreset quirks on these controllers, I think this is as good as it
can get.

Tested on mcp5x (swncq), nf3 and ck804 for all both boot, warm and
hot probing cases.

Kudos to all the bug reporters and their painful hours with these damn
controllers.  ;-)

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Robert Hancock <hancockr@shaw.ca>
Reported-by: David Lang <david@lang.hm>
Reported-by: Samo Vodopivec <lament.email.si@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>