add support for NCQ on Gen IIe hardware

mvsata_quetag_get()/put() pairs adjusted to work also for non-DMA code paths,
i.e. during probe; replaced wdcintr() call with local routine which uses
currently active command tag, rather than assuming always tag 0 on that
code path

~55MB/s -> ~80MB/s sequential read using fio(1) on a test HDD, quite nice

(jdolecek)