Build the UART drivers for the postcar stage. TEST=Build and run on Galileo Gen2 Change-Id: I8bf51135ab7e62fa4bc3e8d45583f2feac56942f Signed-off-by: Lee Leahy <leroy.p.leahy@intel.com> Reviewed-on: https://review.coreboot.org/15843 Tested-by: build bot (Jenkins) Reviewed-by: Aaron Durbin <adurbin@chromium.org>