Allow selecting the physical USB Debug Port on AMD SB700.

Allow selecting the physical USB Debug Port on AMD SB700.

The AMD SB700 allows changing the physical USB port to be used as
USB Debug Port, implement support for this.

Also, fix incorrect PCI device of the SB700 EHCI device. Actually, the
SB700 has _two_ EHCI devices (D18:F2 and D19:F2), but for now we only use
D18:F2. Our generic USBDEBUG code cannot handle multiple EHCI PCI devices
currently, AFAICS.

Hook up all SB700 boards to the CONFIG_USBDEBUG_DEFAULT_PORT facility.

Untested, but should work.

Signed-off-by: Uwe Hermann <uwe@hermann-uwe.de>
Acked-by: Peter Stuge <peter@stuge.se>
git-svn-id: svn://svn.coreboot.org/coreboot/trunk@5907 2b7e53f0-3cfb-0310-b3e9-8179ed1497e1