Rename some defines containing FAT in their name to be filesystem generic

Rename some defines containing FAT in their name to be filesystem generic:
MMCSD_MODE_FAT => MMCSD_MODE_FS
CONFIG_SPL_FAT_LOAD_ARGS_NAME => CONFIG_SPL_FS_LOAD_ARGS_NAME
CONFIG_SPL_FAT_LOAD_PAYLOAD_NAME => CONFIG_SPL_FS_LOAD_PAYLOAD_NAME
CONFIG_SYS_MMC_SD_FAT_BOOT_PARTITION => CONFIG_SYS_MMC_SD_FS_BOOT_PARTITION

Signed-off-by: Guillaume GARDET <guillaume.gardet@free.fr>
Cc: Tom Rini <trini@ti.com>
diff --git a/arch/arm/cpu/at91-common/spl.c b/arch/arm/cpu/at91-common/spl.c
index cbb5a52..674a470 100644
--- a/arch/arm/cpu/at91-common/spl.c
+++ b/arch/arm/cpu/at91-common/spl.c
@@ -102,7 +102,7 @@
 	switch (spl_boot_device()) {
 #ifdef CONFIG_SYS_USE_MMC
 	case BOOT_DEVICE_MMC1:
-		return MMCSD_MODE_FAT;
+		return MMCSD_MODE_FS;
 		break;
 #endif
 	case BOOT_DEVICE_NONE: