Kconfig: SPL_FIT_SIGNATURE requires SPL_LOAD_FIT

Having the ability to support firmware FIT signatures on the SPL sounds
not so useful if the SPL is not supporting to load a (U-boot) firmware
as a FIT image.

Signed-off-by: Klaus Heinrich Kiwi <klaus@linux.vnet.ibm.com>

common/Kconfig.boot

@@ -181,6 +181,7 @@ config SPL_FIT_FULL_CHECK
 config SPL_FIT_SIGNATURE
 	bool "Enable signature verification of FIT firmware within SPL"
 	depends on SPL_DM
+	depends on SPL_LOAD_FIT || SPL_LOAD_FIT_FULL
 	select FIT_SIGNATURE
 	select SPL_FIT
 	select SPL_CRYPTO_SUPPORT