Implement new EH.  The exported interface is ata_do_eh() which is to
be called from ->error_handler and performs the following steps to
recover the failed port.

ata_eh_autopsy() : analyze SError/TF, determine the cause of failure
		   and required recovery actions and record it in
		   ap->eh_context
ata_eh_report()	 : report the failure to user
ata_eh_recover() : perform recovery actions described in ap->eh_context
ata_eh_finish()	 : finish failed qcs

LLDDs can customize error handling by modifying eh_context before
calling ata_do_eh() or, if necessary, doing so inbetween each major
steps by calling each step explicitly.
Signed-off-by: NTejun Heo <htejun@gmail.com>