configs: Move CONFIG_FIT_SIGNATURE to defconfig

For the platforms which use,CONFIG_FIT_SIGNATURE, the required configs are
moved to the platform's defconfig file. Selecting CONFIG_FIT_SIGNATURE using
defconfig automatically resolves the dependencies for signature verification.
The RSA library gets automatically selected and user does not have to define
CONFIG_RSA manually.

Signed-off-by: Ruchika Gupta <ruchika.gupta@freescale.com>
CC: Simon Glass <sjg@chromium.org>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/zynq_zybo_defconfig b/configs/zynq_zybo_defconfig
index 12311cd..9183629 100644
--- a/configs/zynq_zybo_defconfig
+++ b/configs/zynq_zybo_defconfig
@@ -4,3 +4,6 @@
 +S:CONFIG_TARGET_ZYNQ_ZYBO=y
 CONFIG_OF_CONTROL=y
 CONFIG_DEFAULT_DEVICE_TREE="zynq-zybo"
+CONFIG_FIT=y
+CONFIG_FIT_VERBOSE=y
+CONFIG_FIT_SIGNATURE=y