feat(rme): add dummy realm attestation key to RMMD

Add a dummy realm attestation key to RMMD, and return it on request.
The realm attestation key is requested with an SMC with the following
parameters:
    * Fid (0xC400001B2).
    * Attestation key buffer PA (the realm attestation key is copied
      at this address by the monitor).
    * Attestation key buffer length as input and size of realm
      attesation key as output.
    * Type of elliptic curve.

Signed-off-by: Tamas Ban <tamas.ban@arm.com>
Signed-off-by: Subhasish Ghosh <subhasish.ghosh@arm.com>
Signed-off-by: Soby Mathew <soby.mathew@arm.com>
Change-Id: I12d8d98fd221f4638ef225c9383374ddf6e65eac
diff --git a/services/std_svc/rmmd/rmmd_private.h b/services/std_svc/rmmd/rmmd_private.h
index d7ef4e1..73df2b8 100644
--- a/services/std_svc/rmmd/rmmd_private.h
+++ b/services/std_svc/rmmd/rmmd_private.h
@@ -54,6 +54,8 @@
 /* Functions implementing attestation utilities for RMM */
 int rmmd_attest_get_platform_token(uint64_t buf_pa, uint64_t *buf_len,
 				   uint64_t challenge_hash_len);
+int rmmd_attest_get_signing_key(uint64_t buf_pa, uint64_t *buf_len,
+				   uint64_t ecc_curve);
 
 /* Assembly helpers */
 uint64_t rmmd_rmm_enter(uint64_t *c_rt_ctx);