Correct SPL uses of FEC_MXC

This converts 4 usages of this option to the non-SPL form, since there is
no SPL_FEC_MXC defined in Kconfig

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/board/engicam/imx8mp/icore_mx8mp.c b/board/engicam/imx8mp/icore_mx8mp.c
index f0096a2..500080c 100644
--- a/board/engicam/imx8mp/icore_mx8mp.c
+++ b/board/engicam/imx8mp/icore_mx8mp.c
@@ -58,7 +58,7 @@
 
 int board_init(void)
 {
-	if (CONFIG_IS_ENABLED(FEC_MXC))
+	if (IS_ENABLED(CONFIG_FEC_MXC))
 		setup_fec();
 
 	if (IS_ENABLED(CONFIG_DWC_ETH_QOS))
diff --git a/board/freescale/imx8mp_evk/imx8mp_evk.c b/board/freescale/imx8mp_evk/imx8mp_evk.c
index c769267..ce211d4 100644
--- a/board/freescale/imx8mp_evk/imx8mp_evk.c
+++ b/board/freescale/imx8mp_evk/imx8mp_evk.c
@@ -55,7 +55,7 @@
 {
 	int ret = 0;
 
-	if (CONFIG_IS_ENABLED(FEC_MXC)) {
+	if (IS_ENABLED(CONFIG_FEC_MXC)) {
 		setup_fec();
 	}
 
diff --git a/board/freescale/imx93_evk/imx93_evk.c b/board/freescale/imx93_evk/imx93_evk.c
index e01b2f5..e73a4987 100644
--- a/board/freescale/imx93_evk/imx93_evk.c
+++ b/board/freescale/imx93_evk/imx93_evk.c
@@ -66,7 +66,7 @@
 
 int board_init(void)
 {
-	if (CONFIG_IS_ENABLED(FEC_MXC))
+	if (IS_ENABLED(CONFIG_FEC_MXC))
 		setup_fec();
 
 	if (IS_ENABLED(CONFIG_DWC_ETH_QOS))
diff --git a/board/variscite/imx8mn_var_som/imx8mn_var_som.c b/board/variscite/imx8mn_var_som/imx8mn_var_som.c
index e274e0e..d40f4d0 100644
--- a/board/variscite/imx8mn_var_som/imx8mn_var_som.c
+++ b/board/variscite/imx8mn_var_som/imx8mn_var_som.c
@@ -18,7 +18,7 @@
 
 int board_init(void)
 {
-	if (CONFIG_IS_ENABLED(FEC_MXC))
+	if (IS_ENABLED(CONFIG_FEC_MXC))
 		setup_fec();
 
 	return 0;