Documentation: fix \p used for non-parameters

In Doxygen documentation, use \c rather than \p when discussing
something that isn't a parameter of the current macro or function.
Where needed, explain what the thing is.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

include/psa/crypto.h

@@ -3465,7 +3465,8 @@ psa_status_t psa_key_derivation_output_bytes(
  * state and must be aborted by calling psa_key_derivation_abort().
  *
  * How much output is produced and consumed from the operation, and how
- * the key is derived, depends on the key type:
+ * the key is derived, depends on the key type and on the key size
+ * (denoted \c bits below):
  *
  * - For key types for which the key is an arbitrary sequence of bytes
  *   of a given size, this function is functionally equivalent to
@@ -3475,7 +3476,7 @@ psa_status_t psa_key_derivation_output_bytes(
  *   if the implementation provides an isolation boundary then
  *   the key material is not exposed outside the isolation boundary.
  *   As a consequence, for these key types, this function always consumes
- *   exactly (\p bits / 8) bytes from the operation.
+ *   exactly (\c bits / 8) bytes from the operation.
  *   The following key types defined in this specification follow this scheme:
  *
  *     - #PSA_KEY_TYPE_AES;
@@ -3496,8 +3497,8 @@ psa_status_t psa_key_derivation_output_bytes(
  *       string and process it as specified in RFC 7748 §5.
  *
  * - For key types for which the key is represented by a single sequence of
- *   \p bits bits with constraints as to which bit sequences are acceptable,
- *   this function draws a byte string of length (\p bits / 8) bytes rounded
+ *   \c bits bits with constraints as to which bit sequences are acceptable,
+ *   this function draws a byte string of length (\c bits / 8) bytes rounded
  *   up to the nearest whole number of bytes. If the resulting byte string
  *   is acceptable, it becomes the key, otherwise the drawn bytes are discarded.
  *   This process is repeated until an acceptable byte string is drawn.

include/psa/crypto_se_driver.h

@@ -1061,7 +1061,8 @@ typedef psa_status_t (*psa_drv_se_export_key_t)(psa_drv_se_context_t *drv_contex
  * \brief A function that generates a symmetric or asymmetric key on a secure
  * element
  *
- * If \p type is asymmetric (#PSA_KEY_TYPE_IS_ASYMMETRIC(\p type) = 1),
+ * If the key type \c type recorded in \p attributes
+ * is asymmetric (#PSA_KEY_TYPE_IS_ASYMMETRIC(\c type) = 1),
  * the driver may export the public key at the time of generation,
  * in the format documented for psa_export_public_key() by writing it
  * to the \p pubkey buffer.

include/psa/crypto_sizes.h

@@ -190,7 +190,7 @@
 
 /** This macro returns the maximum supported length of the PSK for the
  * TLS-1.2 PSK-to-MS key derivation
- * (#PSA_ALG_TLS12_PSK_TO_MS(\p hash_alg)).
+ * (#PSA_ALG_TLS12_PSK_TO_MS(\c hash_alg)).
  *
  * The maximum supported length does not depend on the chosen hash algorithm.
  *