Convert CONFIG_SYS_TIMER_COUNTS_DOWN to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_TIMER_COUNTS_DOWN

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/lib/Kconfig b/lib/Kconfig
index 6abe1d0..c39fc52 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -15,6 +15,9 @@
 	help
 	  Sets the number of entries in the virtual-physical mapping table.
 
+config SYS_TIMER_COUNTS_DOWN
+	bool "System timer counts down rathe than up"
+
 config PHYSMEM
 	bool "Access to physical memory region (> 4G)"
 	help