FIT: Modify option FIT_SIGNATURE in Kconfig

For FIT signature based approach to work, RSA library needs to be selected.
The FIT_SIGNATURE option in Kconfig is modified to automatically select RSA.
Selecting RSA compiles the RSA library required for image verification.

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/Kconfig b/Kconfig
index 4157da3..fed488f 100644
--- a/Kconfig
+++ b/Kconfig
@@ -116,8 +116,9 @@
 	depends on FIT
 
 config FIT_SIGNATURE
-	bool "Enabel signature verification of FIT uImages"
+	bool "Enable signature verification of FIT uImages"
 	depends on FIT
+	select RSA
 	help
 	  This option enables signature verification of FIT uImages,
 	  using a hash signed and verified using RSA.