ata: avoid probing NCQ Prio Support if not explicitly requested

Previously, when the ata device was being initialized we were
probing for NCQ prio support by checking the identify information
and also checking the log page that holds information about ncq prio
support.

This caused an error on an Intel HBA so the code is now updated to
only probe for NCQ prio support when the sysfs variable controlling
NCQ prio support is enabled.

tj: Update formatting, switch to spin_[un]lock_irq() and update
    locking a bit, use REVALIDATE instead of RESET, and return -EIO
    instead of -EINVAL on config failure.

Signed-off-by: Adam Manzanares <adam.manzanares@wdc.com>
Signed-off-by: Tejun Heo <tj@kernel.org>