[U-Boot] [PATCH 16/45] serial: Allow serial to be absent in TPL

[sjg at google.com]

At present this option applies to SPL, but it should be available in TPL
also, and separately. Change to using CONFIG_IS_ENABLED(), add a new
Kconfig option and fix up hang().

Signed-off-by: Simon Glass <sjg at chromium.org>
---

 drivers/serial/Kconfig         | 10 ++++++++++
 drivers/serial/serial-uclass.c |  4 ++++
 lib/hang.c                     |  5 +++--
 3 files changed, 17 insertions(+), 2 deletions(-)

Applied to u-boot-dm