usb: Add CFG_OHCI_USE_NPS to common USB-OHCI driver

This patch adds CFG_OHCI_USE_NPS to the common USB-OHCI driver. This
way a board just needs to define this new option to enable the "force
NoPowerSwitching mode" instead of adding new CPU/architecture defines
to the USB source itself.

This new option will be used first with the new AMCC 460EX Canyonlands
board port, which will be posted in a few days.

This patch also fixes a small compilation problem when DEBUG is enabled.

Signed-off-by: Stefan Roese <sr@denx.de>