Move attribute fields to a substructure

Move the "core attributes" to a substructure of psa_key_attribute_t.
The motivation is to be able to use the new structure
psa_core_key_attributes_t internally.
diff --git a/library/psa_crypto_se.c b/library/psa_crypto_se.c
index aece47d..58b0f38 100644
--- a/library/psa_crypto_se.c
+++ b/library/psa_crypto_se.c
@@ -198,7 +198,7 @@
     psa_drv_se_allocate_key_t p_allocate = NULL;
 
     /* If the lifetime is wrong, it's a bug in the library. */
-    if( driver->lifetime != attributes->lifetime )
+    if( driver->lifetime != psa_get_key_lifetime( attributes ) )
         return( PSA_ERROR_CORRUPTION_DETECTED );
 
     /* If the driver doesn't support key creation in any way, give up now. */