libata: Add helper to determine when PHY events should be ignored

This is a preparation commit that will allow to add other criteria
according to which PHY events should be dropped.

Signed-off-by: Gabriele Mazzotta <gabriele.mzt@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: stable@vger.kernel.org

diff --cc drivers/ata/libahci.c
Simple merge

diff --cc drivers/ata/libata-core.c
Simple merge

diff --cc include/linux/libata.h
Simple merge