arm: kirkwood: Enable Debug UART for Zyxel NSA310S

It's useful to enable Debug UART for future DM Serial regression tests
for Kirkwood boards.

Also, see background discussion in this thread:
https://lists.denx.de/pipermail/u-boot/2023-March/512010.html

Signed-off-by: Tony Dinh <mibodhi@gmail.com>
Reviewed-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Stefan Roese <sr@denx.de>
diff --git a/configs/nsa310s_defconfig b/configs/nsa310s_defconfig
index 76839e6..b936ae1 100644
--- a/configs/nsa310s_defconfig
+++ b/configs/nsa310s_defconfig
@@ -15,8 +15,11 @@
 CONFIG_ENV_OFFSET=0xE0000
 CONFIG_DEFAULT_DEVICE_TREE="kirkwood-nsa310s"
 CONFIG_SYS_PROMPT="NSA310s> "
+CONFIG_DEBUG_UART_BASE=0xf1012000
+CONFIG_DEBUG_UART_CLOCK=166666667
 CONFIG_IDENT_STRING="\nZyXEL NSA310S/320S 1/2-Bay Power Media Server"
 CONFIG_SYS_LOAD_ADDR=0x800000
+CONFIG_DEBUG_UART=y
 CONFIG_DISTRO_DEFAULTS=y
 CONFIG_BOOTDELAY=3
 CONFIG_USE_PREBOOT=y
@@ -50,6 +53,7 @@
 CONFIG_PHY_MARVELL=y
 CONFIG_MVGBE=y
 CONFIG_MII=y
+CONFIG_DEBUG_UART_SHIFT=2
 CONFIG_USB=y
 CONFIG_USB_EHCI_HCD=y
 CONFIG_UBIFS_SILENCE_MSG=y