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/mx6sabreauto_defconfig b/configs/mx6sabreauto_defconfig
index 0c7aaa6..053026d 100644
--- a/configs/mx6sabreauto_defconfig
+++ b/configs/mx6sabreauto_defconfig
@@ -32,7 +32,7 @@
 # CONFIG_CONSOLE_MUX is not set
 CONFIG_SYS_CONSOLE_IS_IN_ENV=y
 CONFIG_SYS_CONSOLE_OVERWRITE_ROUTINE=y
-CONFIG_SPL_LEGACY_IMAGE_SUPPORT=y
+CONFIG_SPL_LEGACY_IMAGE_FORMAT=y
 CONFIG_SPL_FIT_IMAGE_TINY=y
 CONFIG_SPL_FS_EXT4=y
 CONFIG_SPL_I2C=y