Kconfig: SPL_FIT_SIGNATURE selects FIT_SIGNATURE

Selecting SPL_FIT_SIGNATURE (without selecting U-boot proper
verified boot first) breaks the build due to
CONFIG_FIT_SIGNATURE_MAX_SIZE being undefined, in addition to Kconfig
warnings on RSA and IMAGE_SIGN_INFO unmet dependencies.

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
+	select FIT_SIGNATURE
 	select SPL_FIT
 	select SPL_CRYPTO_SUPPORT
 	select SPL_HASH_SUPPORT