crypto: ecdh - add privkey generation support

Add support for generating ecc private keys.

Generation of ecc private keys is helpful in a user-space to kernel
ecdh offload because the keys are not revealed to user-space. Private
key generation is also helpful to implement forward secrecy.

If the user provides a NULL ecc private key, the kernel will generate it
and further use it for ecdh.

Move ecdh's object files below drbg's. drbg must be present in the kernel
at the time of calling.

Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Reviewed-by: Stephan Müller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/Kconfig

@@ -130,6 +130,7 @@ config CRYPTO_DH
 config CRYPTO_ECDH
 	tristate "ECDH algorithm"
 	select CRYTPO_KPP
+	select CRYPTO_RNG_DEFAULT
 	help
 	  Generic implementation of the ECDH algorithm