DM: crypto/rsa_mod_exp: Add rsa Modular Exponentiation DM driver

Add a new rsa uclass for performing modular exponentiation and implement
the software driver basing on this uclass.

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/drivers/crypto/Makefile b/drivers/crypto/Makefile
index 7b79237..fb8c10b 100644
--- a/drivers/crypto/Makefile
+++ b/drivers/crypto/Makefile
@@ -6,4 +6,5 @@
 #
 
 obj-$(CONFIG_EXYNOS_ACE_SHA)	+= ace_sha.o
+obj-y += rsa_mod_exp/
 obj-y += fsl/