spl: sata: don't force FS_FAT support

Allow the code to build when FS_FAT is not enabled, and thus
spl_load_image_fat() is not provided.

A subsequent patch should add alternative raw access U-Boot main image
load method.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Stefan Roese <sr@denx.de>
diff --git a/common/spl/spl_sata.c b/common/spl/spl_sata.c
index 2fb4610..f0af9f3 100644
--- a/common/spl/spl_sata.c
+++ b/common/spl/spl_sata.c
@@ -53,9 +53,13 @@
 				  CONFIG_SYS_SATA_FAT_BOOT_PARTITION))
 #endif
 	{
-		err = spl_load_image_fat(spl_image, stor_dev,
+		err = -ENOSYS;
+
+		if (IS_ENABLED(CONFIG_SPL_FS_FAT)) {
+			err = spl_load_image_fat(spl_image, stor_dev,
 					CONFIG_SYS_SATA_FAT_BOOT_PARTITION,
-				CONFIG_SPL_FS_LOAD_PAYLOAD_NAME);
+					CONFIG_SPL_FS_LOAD_PAYLOAD_NAME);
+		}
 	}
 	if (err) {
 		puts("Error loading sata device\n");