add new function for opaque data parsing.

[jyao1]

libspdm_get_element_from_opaque_data() will get first (element_id, and sm_data_id) pair. Although the name is generic, but it has assumption that element_id is DMTF, because sm_data_id is only under DMTF.

I suggest to define two functions: (just rough thought)

• libspdm_get_element_from_opaque_data_with_element_id (element_id, element_index) - that is to get element with ID and index to support multiple elements.
• libspdm_get_sm_data_element_from_opaque_data (sm_data_id) - that is to get SM_DATA only, with assumption that element_id is DMTF.

The first function can be used for SPDM 1.4 with DMTF-DSP, and support DSP0289 Authorization AODS.

• libspdm_get_aods_element_from_opaque_data (aods_id) - that is to get AODS with assumption that element_id is DMTF-DSP in the future.

Ref: #2935 (comment)