lib: rsa: decouple rsa from FIT image verification

Introduce new configuration, CONFIG_RSA_VERIFY which will decouple building
RSA functions from FIT verification and allow for adding a RSA-based
signature verification for other file formats, in particular PE file
for UEFI secure boot.

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/Makefile b/tools/Makefile
index 99be724..3b9ae90 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -58,7 +58,7 @@
 hostprogs-$(CONFIG_CMD_BOOTEFI_SELFTEST) += file2include
 
 FIT_OBJS-$(CONFIG_FIT) := fit_common.o fit_image.o image-host.o common/image-fit.o
-FIT_SIG_OBJS-$(CONFIG_FIT_SIGNATURE) := common/image-sig.o
+FIT_SIG_OBJS-$(CONFIG_FIT_SIGNATURE) := common/image-sig.o common/image-fit-sig.o
 FIT_CIPHER_OBJS-$(CONFIG_FIT_CIPHER) := common/image-cipher.o
 
 # The following files are synced with upstream DTC.