tpm: rng: Add driver model interface for TPM RNG device

The TPM device has a builtin random number generator(RNG)
functionality. Expose the RNG functions of the TPM device to the
driver model so that they can be used by the EFI_RNG_PROTOCOL if the
protocol is installed.

Also change the function arguments and return type of the random
number functions to comply with the driver model api.

Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
diff --git a/drivers/rng/Kconfig b/drivers/rng/Kconfig
index 21a9ff0..1614368 100644
--- a/drivers/rng/Kconfig
+++ b/drivers/rng/Kconfig
@@ -74,4 +74,13 @@
 	  Enable random number generator for platforms that support Arm
 	  SMCCC TRNG interface.
 
+config TPM_RNG
+	bool "Enable random number generator on TPM device"
+	depends on TPM
+	default y
+	help
+	  The TPM device has an inbuilt random number generator
+	  functionality. Enable random number generator on TPM
+	  devices.
+
 endif