Rename generator functions to psa_key_derivation_xxx

Generators are mostly about key derivation (currently: only about key
derivation). "Generator" is not a commonly used term in cryptography.
So favor "derivation" as terminology. Call a generator a key
derivation operation structure, since it behaves like other multipart
operation structures. Furthermore, the function names are not fully
consistent.

In this commit, I rename the functions to consistently have the prefix
"psa_key_derivation_". I used the following command:

    perl -i -pe '%t = (
        psa_crypto_generator_t => "psa_key_derivation_operation_t",
        psa_crypto_generator_init => "psa_key_derivation_init",
        psa_key_derivation_setup => "psa_key_derivation_setup",
        psa_key_derivation_input_key => "psa_key_derivation_input_key",
        psa_key_derivation_input_bytes => "psa_key_derivation_input_bytes",
        psa_key_agreement => "psa_key_derivation_key_agreement",
        psa_set_generator_capacity => "psa_key_derivation_set_capacity",
        psa_get_generator_capacity => "psa_key_derivation_get_capacity",
        psa_generator_read => "psa_key_derivation_output_bytes",
        psa_generate_derived_key => "psa_key_derivation_output_key",
        psa_generator_abort => "psa_key_derivation_abort",
        PSA_CRYPTO_GENERATOR_INIT => "PSA_KEY_DERIVATION_OPERATION_INIT",
        PSA_GENERATOR_UNBRIDLED_CAPACITY => "PSA_KEY_DERIVATION_UNLIMITED_CAPACITY",
        ); s/\b(@{[join("|", keys %t)]})\b/$t{$1}/ge' $(git ls-files)
diff --git a/include/psa/crypto_struct.h b/include/psa/crypto_struct.h
index df76571..74e362d 100644
--- a/include/psa/crypto_struct.h
+++ b/include/psa/crypto_struct.h
@@ -240,10 +240,10 @@
     } ctx;
 };
 
-#define PSA_CRYPTO_GENERATOR_INIT {0, 0, {{0, 0}}}
-static inline struct psa_crypto_generator_s psa_crypto_generator_init( void )
+#define PSA_KEY_DERIVATION_OPERATION_INIT {0, 0, {{0, 0}}}
+static inline struct psa_crypto_generator_s psa_key_derivation_operation_init( void )
 {
-    const struct psa_crypto_generator_s v = PSA_CRYPTO_GENERATOR_INIT;
+    const struct psa_crypto_generator_s v = PSA_KEY_DERIVATION_OPERATION_INIT;
     return( v );
 }