Pass FC type along for all FFN types

[dakinggg]

Previously, we were accidentally setting the ffn_config to the ffn_config_defaults dictionary directly. This meant that the modification of self.ffn_config here (

llm-foundry/llmfoundry/models/mpt/configuration_mpt.py

Line 316 in 994209c

self.ffn_config['fc_type'] = self.fc_type

) could potentially alter the defaults dictionary. This led to unexpected results if the constructor is called multiple times (which it is, during the HF construction process, internally to huggingface code). The result was the fc_type was always added to the ffn_config. With the recent overhaul of the config system, we altered this behavior by calling the constructor directly instead of from_dict, removing the extra construction call that was modifying the defaults.

This PR therefore does two things:
(1) Passes fc_type along to all ffn construction functions
(2) fixes the dangerous dictionary default setting in the MPT config class