Upcoming changes to structure of Intel SGX-related GitHub repositories

[bgotowal]

We are making the following changes to the structure of Intel SGX-related GitHub repositories to facilitate more efficient collaboration with the community and improve the consumption of our code:

1. SGX SDK (/sdk dir) has been 🚚 moved to intel/confidential-computing.sgx.sdk as part of the SGX 2.30 release.
   The SGX repository references it via a Git submodule.

2. AESM codebase (/psw dir and supporting build/packaging infrastructure) will be 🚚 moved to a standalone GitHub repository.
   The SGX repository will reference it via a Git submodule.

3. Longer-term, non-SGX-specific DCAP components will be decoupled from the SGX build system and built independently in their own repositories.

This is a source-code layout change only. Binary deliverables, APIs and packaging are unaffected — if you consume the released binaries or distribution packages, no action is required. If you build from source, clone recursively (--recurse-submodules) to pull the relocated sources. If you haven't utilized submodules before, please ensure you run git submodule update --init after cloning.

Please let us know of any concerns. For background on the motivation, see the original discussion on the DCAP repository.