spl: Rename Kconfig SPL_LEGACY_IMAGE_SUPPORT to SPL_LEGACY_IMAGE_FORMAT

This matches what this support is called in the non-SPL case. The postfix
_SUPPORT is redundant as enabling Kconfig options implies support.
With this we can use CONFIG_IS_ENABLED() as needed.

Signed-off-by: Andrew Davis <afd@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/taurus_defconfig b/configs/taurus_defconfig
index c24b448..e6bef6c 100644
--- a/configs/taurus_defconfig
+++ b/configs/taurus_defconfig
@@ -39,7 +39,7 @@
 CONFIG_BOOTCOMMAND="nand read 0x22000000 0x200000 0x300000; bootm"
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_BOARD_EARLY_INIT_F=y
-# CONFIG_SPL_LEGACY_IMAGE_SUPPORT is not set
+# CONFIG_SPL_LEGACY_IMAGE_FORMAT is not set
 CONFIG_SPL_SYS_MALLOC_SIMPLE=y
 CONFIG_SPL_CRC32=y
 CONFIG_SPL_NAND_SUPPORT=y