[U-Boot] [PATCH v3 2/2] serial: atmel_usart: Add clk support

[sjg at google.com]

Add the clock support.
Note that the clock handling of the DBGU peripheral is different
from the USART.

Signed-off-by: Wenyou Yang <wenyou.yang at atmel.com>
Reviewed-by: Simon Glass <sjg at chromium.org>
---

Changes in v3:
 - Rebase on the master branch (22e10be45) of u-boot-dm git tree.

Changes in v2:
 - Fix the DBGU clock handling.
 - Add Reviewed-by tag.

 drivers/serial/atmel_usart.c | 52 +++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 49 insertions(+), 3 deletions(-)

Applied to u-boot-dm/next, thanks!