docs: enhance crypto documentation with key management features

Add detailed documentation for:
- MTD-based key storage and persistence
- AES key generation with multiple key sizes
- ECC P-256 key pair generation for ECDSA operations
- Key lifecycle management (save/load/delete)

Signed-off-by: makejian <makejian@xiaomi.com>

Documentation/components/crypto.rst

@@ -186,3 +186,46 @@ The cryptodev module supports RSA digital signatures via the cryptokey interface
   - Output: verification result
 
 Both padding schemes are supported via the cryptokey ioctl interface accessible through ``/dev/crypto``.
+
+Key Management Operations
+--------------------------
+
+The cryptodev module provides comprehensive key management interfaces:
+
+**Key Generation**
+
+- CRK_GENERATE_AES_KEY: Generate AES key data with specified key ID
+  - Supports 128-bit, 192-bit, and 256-bit key generation
+  - Generates cryptographically secure random AES keys using software implementation
+  - Keys can be used immediately for AES encryption/decryption operations
+
+- CRK_GENERATE_RSA_KEY: Generate RSA keypair (public and private) with specified key ID
+- CRK_GENERATE_SECP256R1_KEY: Generate ECDSA keypair on SECP256R1 curve with specified key ID
+  - Generates P-256 elliptic curve keypairs for ECDSA operations
+  - Uses NuttX's lightweight ECC implementation for key generation
+  - Generated keys can be used for ECDSA digital signature operations
+
+**Key Lifecycle Management**
+
+- CRK_DELETE_KEY: Remove key with specified key ID from the driver
+- CRK_SAVE_KEY: Persist key data to FLASH storage for non-volatile storage
+- CRK_LOAD_KEY: Load previously saved key data from FLASH into RAM
+
+**MTD-based Key Storage**
+
+NuttX supports persistent key storage using MTD (Memory Technology Device):
+
+- Keys can be saved to MTD-based storage for non-volatile persistence
+- Software-based key management (swkey) provides transparent MTD integration
+- Keys are automatically loaded from MTD upon system initialization
+- Supports both symmetric (AES) and asymmetric (RSA, ECC) key storage
+- Enables secure device configuration and credential persistence across reboots
+
+**Cryptographic Operations Using Keys**
+
+Once keys are allocated, generated, or imported, they can be used for:
+
+- Symmetric encryption/decryption operations (AES)
+- RSA signature generation and verification
+- ECDSA digital signature operations
+- Key exchange protocols