board: sl28: add config to enable console output on SER0

Sometimes it is desireable to have the console output on the first
serial line. Introduce a configuration option for it (in the board
scope).

Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>
diff --git a/board/kontron/sl28/Kconfig b/board/kontron/sl28/Kconfig
index 4078ef1..abcacc3 100644
--- a/board/kontron/sl28/Kconfig
+++ b/board/kontron/sl28/Kconfig
@@ -48,4 +48,14 @@
 
 endif
 
+config SL28_ENABLE_SER0_CONSOLE
+	bool "Enable console output on SER0"
+	select DM_SERIAL
+	select SPL_DM_SERIAL
+	select FSL_LPUART
+	help
+	  By default the console output of this board is on the second serial
+	  line (SER1). Sometimes it is desirable to enable output on the first
+	  serial line (SER0). For example, if you have a carrier which only
+	  supports the first serial port.
 endif