arm: mvebu: clearfog: Add option for 2.5 Gbps SFP

While newer Linux kernels provide autoconfiguration of SFP, provide
an option for setting in U-Boot Kconfig for use prior to booting.

Signed-off-by: Joel Johnson <mrjoel@lixil.net>
Reviewed-by: Stefan Roese <sr@denx.de>
diff --git a/board/solidrun/clearfog/Kconfig b/board/solidrun/clearfog/Kconfig
index 936d591..c910e17 100644
--- a/board/solidrun/clearfog/Kconfig
+++ b/board/solidrun/clearfog/Kconfig
@@ -15,4 +15,11 @@
 	  detection via additional EEPROM hardware. This option enables selecting
 	  the Base variant for older hardware revisions.
 
+config CLEARFOG_SFP_25GB
+	bool "Enable 2.5 Gbps mode for SFP"
+	help
+	  Set the SFP module connection to support 2.5 Gbps transfer speed for the
+	  SGMII connection (requires a supporting SFP). By default, transfer speed
+	  of 1.25 Gbps is used, suitable for a more common 1 Gbps SFP module.
+
 endmenu
diff --git a/board/solidrun/clearfog/clearfog.c b/board/solidrun/clearfog/clearfog.c
index 11d3a7f..8f3e5dc 100644
--- a/board/solidrun/clearfog/clearfog.c
+++ b/board/solidrun/clearfog/clearfog.c
@@ -63,6 +63,11 @@
 {
 	cf_read_tlv_data();
 
+	/* Apply build configuration options before runtime configuration */
+	if (IS_ENABLED(CONFIG_CLEARFOG_SFP_25GB))
+		board_serdes_map[5].serdes_speed = SERDES_SPEED_3_125_GBPS;
+
+	/* Apply runtime detection changes */
 	if (sr_product_is(&cf_tlv_data, "Clearfog GTR")) {
 		board_serdes_map[0].serdes_type = PEX0;
 		board_serdes_map[0].serdes_speed = SERDES_SPEED_5_GBPS;