[ARM] Orion: add the option to support different ehci phy initialization

The Orion ehci driver serves the Orion, kirkwood and DD Soc families.
Since each of those integrate a different USB phy we should have the
ability to use few initialization sequences or to leave the boot loader
phy settings as is.

Signed-off-by: Ronen Shitrit <rshitrit@marvell.com>