Kconfig: fix SPL_FIT dependency

SPL_FIT obviously requires libfdt in SPL, so let Kconfig express that by
selecting SPL_OF_LIBFDT.
Also make the actual options that users want (SPL signature and SPL FIT
loading) visible in the menu and let them select the SPL_FIT as a
requirement.
Also remove the now redundant SPL_OF_LIBFDT from those Kconfigs that had
it in for the SPL FIT loading feature.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
[Remove change from configs/evb-rk3399_defconfig]
Signed-off-by: Jagan Teki <jagan@openedev.com>

Kconfig

@@ -208,15 +208,17 @@ config FIT_IMAGE_POST_PROCESS
 config SPL_FIT
 	bool "Support Flattened Image Tree within SPL"
 	depends on SPL
+	select SPL_OF_LIBFDT
 
 config SPL_FIT_SIGNATURE
 	bool "Enable signature verification of FIT firmware within SPL"
-	depends on SPL_FIT
 	depends on SPL_DM
+	select SPL_FIT
 	select SPL_RSA
 
 config SPL_LOAD_FIT
 	bool "Enable SPL loading U-Boot as a FIT"
+	select SPL_FIT
 	help
 	  Normally with the SPL framework a legacy image is generated as part
 	  of the build. This contains U-Boot along with information as to

configs/am335x_evm_defconfig

@@ -48,4 +48,3 @@ CONFIG_G_DNL_MANUFACTURER="Texas Instruments"
 CONFIG_G_DNL_VENDOR_NUM=0x0451
 CONFIG_G_DNL_PRODUCT_NUM=0xd022
 CONFIG_RSA=y
-CONFIG_SPL_OF_LIBFDT=y