qed: Introduce DMA_REGPAIR_LE

FW hsi contains regpairs, mostly for 64-bit address representations.
Since same paradigm is applied each time a regpair is filled, this
introduces a new utility macro for setting such regpairs.

Signed-off-by: Yuval Mintz <Yuval.Mintz@qlogic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>