rng: Add Turris Mox rTWM RNG driver

A RNG driver for Armada 3720 boards running the Turris Mox rWTM firmware
from CZ.NIC in the secure processor.

Signed-off-by: Max Resch <resch.max@gmail.com>
Reviewed-by: Stefan Roese <sr@denx.de>
diff --git a/drivers/rng/Makefile b/drivers/rng/Makefile
index 7e64c4c..ecae1a3 100644
--- a/drivers/rng/Makefile
+++ b/drivers/rng/Makefile
@@ -17,3 +17,4 @@
 obj-$(CONFIG_RNG_ARM_RNDR) += arm_rndr.o
 obj-$(CONFIG_TPM_RNG) += tpm_rng.o
 obj-$(CONFIG_RNG_JH7110) += jh7110_rng.o
+obj-$(CONFIG_RNG_TURRIS_RWTM) += turris_rwtm_rng.o