cracen: safeguard static cracen functions.

Safeguard `cracen_signature_set_hashalgo_from_digestsz()`
and `cracen_signature_set_hashalgo()` inside `PSA_MAX_RSA_KEY_BITS > 0`.

Safeguard `can_sign()` inside
> CONFIG_PSA_WANT_ALG_PURE_EDDSA || `CONFIG_PSA_WANT_ALG_ED25519PH ||
> CONFIG_PSA_WANT_ALG_ECDSA || CONFIG_PSA_WANT_ALG_HMAC

All calls to `cracen_signature_set_hashalgo()` and
`cracen_signature_set_hashalgo_from_digestsz()` are safeguarded in
`PSA_MAX_RSA_KEY_BITS > 0` resulting in unused function warning because
those static functions will never be used when the condition is not met.

Similar for calls to `can_sign()`.
Fixes:
> ...subsys/nrf_security/src/drivers/cracen/cracenpsa/src/sign.c:41:12:
>      warning: unused function
>      'cracen_signature_set_hashalgo' [-Wunused-function]
>    41 | static int cracen_signature_set_hashalgo(...
>       |            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 1 warning generated.

> ...subsys/nrf_security/src/drivers/cracen/cracenpsa/src/sign.c:46:12:
>      warning: unused function
>      'cracen_signature_set_hashalgo_from_digestsz' [-Wunused-function]
>    46 | static int cracen_signature_set_hashalgo_from_digestsz(...
>       |            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 1 warning generated.

> ...subsys/nrf_security/src/drivers/cracen/cracenpsa/src/kmu.c:297:13:
>      warning: unused function 'can_sign' [-Wunused-function]
>   297 | static bool can_sign(const psa_key_attributes_t *key_attr)
>       |             ^~~~~~~~
> 1 warning generated.

Signed-off-by: Torsten Rasmussen <[email protected]>

Author: tejlmand

subsys/nrf_security/src/drivers/cracen/cracenpsa/src/kmu.c

@@ -294,11 +294,14 @@ static psa_status_t get_kmu_slot_id_and_metadata(mbedtls_svc_key_id_t key_id,
 	return read_primary_slot_metadata(*slot_id, metadata);
 }
 
+#if defined(CONFIG_PSA_WANT_ALG_PURE_EDDSA) || defined(CONFIG_PSA_WANT_ALG_ED25519PH) || \
+	defined CONFIG_PSA_WANT_ALG_ECDSA || defined(CONFIG_PSA_WANT_ALG_HMAC)
 static bool can_sign(const psa_key_attributes_t *key_attr)
 {
 	return (psa_get_key_usage_flags(key_attr) & PSA_KEY_USAGE_SIGN_MESSAGE) ||
 	       (psa_get_key_usage_flags(key_attr) & PSA_KEY_USAGE_SIGN_HASH);
 }
+#endif /* defined(CONFIG_PSA_WANT_ALG_PURE_EDDSA) || define(CONFIG_PSA_WANT_ALG_ED25519PH) */
 
 /**
  * @brief Check provisioning state, and delete slots that were not completely provisioned.

subsys/nrf_security/src/drivers/cracen/cracenpsa/src/sign.c

@@ -38,6 +38,7 @@
 #define SI_PSA_IS_KEY_FLAG(flag, attr) ((flag) == (psa_get_key_usage_flags((attr)) & (flag)))
 #define SI_PSA_IS_KEY_TYPE(flag, attr) ((flag) == (psa_get_key_type((attr)) & (flag)))
 
+#if PSA_MAX_RSA_KEY_BITS > 0
 static int cracen_signature_set_hashalgo(const struct sxhashalg **hashalg, psa_algorithm_t alg)
 {
 	return hash_get_algo(PSA_ALG_SIGN_GET_HASH(alg), hashalg);
@@ -81,6 +82,7 @@ static int cracen_signature_set_hashalgo_from_digestsz(const struct sxhashalg **
 
 	return SX_OK;
 }
+#endif /* PSA_MAX_RSA_KEY_BITS > 0 */
 
 static int cracen_signature_prepare_ec_prvkey(struct si_sig_privkey *privkey, char *key_buffer,
 					      size_t key_buffer_size,