Panic flag is move from libata-core to libata-eh module.

Now each channel has its own instance of wait queue to prevent race
conditions when one channel wakes up the queue while the other channel
is processing interrupt and moved its write pointer, but has not
finished all other functions yet (i.e. filling interframe parameters).

This reverts commit 8fc41ee4. Now driver
will wait for sysfs flag to continue loading.