Don't loop infinitely long on serial comm failures

Don't loop infinitely long on serial comm failures

If serial uart (8250/16x50) takes abnormally long to respond, give
up on logging to serial console and instead let the system boot.

Also reference bit in LSR register with correct name.

Change-Id: I3796efc3e8690425f04a130af4bc99541b64d335
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/611
Tested-by: build bot (Jenkins)
Reviewed-by: Peter Stuge <peter@stuge.se>