coreboot: add timer queue implementation

A timer queue provides the mechanism for calling functions
in the future by way of a callback. It utilizes the MONOTONIC_TIMER
to track time through the boot. The implementation is a min-heap
for keeping track of the next-to-expire callback.

Change-Id: Ia56bab8444cd6177b051752342f53b53d5f6afc1
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/3158
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

src/lib/Makefile.inc

@@ -90,6 +90,7 @@ ramstage-$(CONFIG_COLLECT_TIMESTAMPS) += timestamp.c
 ramstage-$(CONFIG_COVERAGE) += libgcov.c
 ramstage-$(CONFIG_MAINBOARD_DO_NATIVE_VGA_INIT) += edid.c
 ramstage-y += memrange.c
+ramstage-$(CONFIG_TIMER_QUEUE) += timer_queue.c
 
 # The CBMEM implementations are chosen based on CONFIG_DYNAMIC_CBMEM.
 ifeq ($(CONFIG_DYNAMIC_CBMEM),y)