phylib: marvell: add support for TX-only and RX-only Internal Delay

Previously, Internal Delay specification implied the delay be
applied to both TX and RX.  This patch allows for separate TX/RX-only
internal delay specification.

Signed-off-by: Kim Phillips <kim.phillips@freescale.com>
Tested-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Acked-by: Li Yang <leoli@freescale.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>