add missing kconfig variables so that refresh does not drop them

Co-authored-by: q66 <daniel@octaforge.org>

board/boundary/nitrogen8m_som/Kconfig

@@ -9,6 +9,18 @@ config SYS_VENDOR
 config SYS_CONFIG_NAME
 	default "nitrogen8m_som"
 
+config DDR_RANK_BITS
+	int "ddr rank bits"
+        default 1
+
+config DDR_CHANNEL_CNT
+	int "ddr channel cnt"
+        default 2
+
+config DDR_DRIVE_STRENGTH
+	int "ddr drive strength"
+	default 6
+
 source "board/boundary/common/Kconfig"
 
 endif