Detect whether the OXPCIE card is really present while in the ROM stage.

Detect whether the OXPCIE card is really present while in the ROM stage.

Use an int in CAR global data to store whether or not the OXPCIE serial card
is actually there. Also, time out if the card doesn't show up quickly enough,
don't continue initialization if it's not there, and don't make the
initialization routine default to a card if none is found.

Change-Id: I9c72d3abc6ee2867b77ab2f2180e6f01f647af8c
Signed-off-by: Gabe Black <gabeblack@google.com>
Reviewed-on: http://review.coreboot.org/728
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>