libata: Add H2D FIS "auxiliary" port flag

Add a new port flag, ATA_FLAG_FPDMA_AUX, used to indicate
support for transmission of the H2D FIS 'auxiliary' field.

Signed-off-by: Marc Carino <marc.ceeeee@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>