Make EHCI power and overcurrent polarities configurable. If not set, these new configurartions keep the default register values so that existing board files do not have to be changed. Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com> Cc: Marek Vasut <marex@denx.de> Cc: Stefano Babic <sbabic@denx.de>