dm: implement a Timer uclass

Implement a Timer uclass to work with lib/time.c.

Signed-off-by: Thomas Chou <thomas@wytron.com.tw>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/Kconfig b/drivers/Kconfig
index c02f323..ba88b5e 100644
--- a/drivers/Kconfig
+++ b/drivers/Kconfig
@@ -58,6 +58,8 @@
 
 source "drivers/thermal/Kconfig"
 
+source "drivers/timer/Kconfig"
+
 source "drivers/tpm/Kconfig"
 
 source "drivers/usb/Kconfig"