libpayload: Tell EHCI to re-enable USB1 controllers

EHCI can take over all ports (and then reroute devices to
companion controllers if needs be). We do that, and then never
reset it.

Consequence:
Systems with only USB1 HC drivers (OHCI/UHCI) never see any devices.

Change-Id: If1d91e9142a6618289b0b3f6b56587ec857158e3
Signed-off-by: Patrick Georgi <patrick.georgi@secunet.com>
Reviewed-on: http://review.coreboot.org/396
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Tested-by: build bot (Jenkins)