[refactor][api] simplify stse_get_ecc_key_type_from_curve_id() signature

[parmi93]

Summary

Reworks stse_get_ecc_key_type_from_curve_id():

• New signature: returns the resolved stse_ecc_key_type_t directly (or STSE_ECC_KT_INVALID if the curve is unknown) and takes a single packed stsafea_ecc_curve_id_t pointer, instead of the previous three parameters (PLAT_UI8 curve_id_length, const PLAT_UI8 *pCurve_id_value, stse_ecc_key_type_t *pKey_type output).
• Guards removed: the #if defined(STSE_CONF_ECC_*) conditional-compilation blocks around the declaration and definition are dropped; the function is now always available.

Why this change

1. Direct interoperability with the slot-info API.
   The curve identifier returned by stse_get_ecc_key_slot_info(), the curve_id field of stsafea_private_key_slot_information_t, is already a stsafea_ecc_curve_id_t. With the old signature the caller had to manually unpack it into a scalar length (length is a 2-byte array) and a value pointer before resolving the key type. The new signature lets that output be passed straight through:

• Before:

  stsafea_private_key_slot_information_t slot_info;
  stse_ecc_key_type_t key_type;
  PLAT_UI16 global_usage_limit;
  
  stse_get_ecc_key_slot_info(pSTSE, slot_number, &global_usage_limit, &slot_info);
  
  /* length is a 2-byte (big-endian) field, had to be reduced to a scalar
   * and split from the value before resolving the key type */
  PLAT_UI8 curve_id_length = slot_info.curve_id.length[1];
  stse_ReturnCode_t ret = stse_get_ecc_key_type_from_curve_id(
      curve_id_length,
      slot_info.curve_id.value,
      &key_type);
  
  if (ret == STSE_OK) {
      /* No point performing this check, because stse_get_ecc_key_type_from_curve_id() 
       * always return STSE_OK */
  }
  
  if (key_type == STSE_ECC_KT_INVALID) {
      /* unrecognized curve */
  }

• After

  stsafea_private_key_slot_information_t slot_info;
  PLAT_UI16 global_usage_limit;
  
  stse_get_ecc_key_slot_info(pSTSE, slot_number, &global_usage_limit, &slot_info);
  
  /* the slot's curve_id can be passed directly */
  stse_ecc_key_type_t key_type = stse_get_ecc_key_type_from_curve_id(&slot_info.curve_id);
  
  if (key_type == STSE_ECC_KT_INVALID) {
      /* unrecognized curve */
  }

2. A clearer, less error-prone contract.
   The function never had a real failure path, it always returned STSE_OK and signalled "not found" through *pKey_type == STSE_ECC_KT_INVALID. Returning the key type directly makes that the single, obvious result value and removes the redundant output pointer and return-code plumbing. The [static 1] array parameter also documents (and, on supporting compilers, enforces) that a non-null pointer is required.

3. Removing the config guards.
   Guarding the symbol behind STSE_CONF_ECC_* made its availability depend on which curves happen to be enabled, so any generic caller had to replicate the same long #if defined(...) condition to avoid link errors. Since the function only reads stse_ecc_info_table and safely returns STSE_ECC_KT_INVALID when no curve matches, there is no reason to compile it out. Exposing it unconditionally gives callers a stable API surface.

Notes

• The byte-for-byte memcmp over the packed struct is safe because stsafea_ecc_curve_id_t is a PLAT_PACKED_STRUCT (no padding between length and value); this is now documented with an inline comment.
• Doxygen documentation and CHANGELOG.md updated to match the new signature.

⚠️ Breaking change: existing callers must be updated to the new signature.