bootcount: allow to use this feature on TPL

This commit add an option TPL_BOOTCOUNT_LIMIT to
use bootcount on TPL.

Signed-off-by: Philippe Reynes <philippe.reynes@softathome.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/Makefile b/drivers/Makefile
index e371bc3..c562a71 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile
@@ -69,6 +69,7 @@
 
 ifdef CONFIG_TPL_BUILD
 
+obj-$(CONFIG_TPL_BOOTCOUNT_LIMIT) += bootcount/
 obj-$(CONFIG_TPL_MPC8XXX_INIT_DDR_SUPPORT) += ddr/fsl/
 
 endif