Update TA implementation to handle SA_KEY_PROVISION_TA command in separate function and file

[mhabrat]

Current SA_KEY_PROVISION_TA command in TA space is implemented within the ta_invoke_key_provision() function rather than in a separate function and file. ta_invoke_key_provision() should include parameter checking and copies to set up the call to the processing function similar to other TA function implementions like ta_sa_key_import(). The ta_sa_key_provision() function should be seperated into its own file (ta_sa_key_provision_ta.c).
Also, looks like the SA_KEY_FORMAT_PROVISION_TA is unnecessary. Can we remove?