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/Kconfig

@@ -318,6 +318,12 @@ config HAVE_MONOTONIC_TIMER
 	help
 	 The board/chipset provides a monotonic timer.
 
+config TIMER_QUEUE
+	def_bool n
+	depends on HAVE_MONOTONIC_TIMER
+	help
+	  Provide a timer queue for performing time-based callbacks. 
+
 config HIGH_SCRATCH_MEMORY_SIZE
 	hex
 	default 0x0