Build remote attestation for UEFI

[jul-sh]

• Applies the UEFI compatibility patch for ring from Add UEFI target support briansmith/ring#1406
• Adds needed build tooling to build ring for a UEFI target
• Includes it as a dep in the UEFI app

[conradgrobler]

I am surprised this does not cause cargo udeps to complain, seeing that the code does not currently use anything from the remote attestation crate. Do we ignore the UEFI app when running cargo udeps?

[jul-sh]

Good catch, forgot about us using cargo udeps. The reason it doesn't complain is that we run it on the workspace, and the UEFI app is excluded from the workspace bc of #2654.

Should we keep this as is? This crate should start actually using this dep fairly soon.

[conradgrobler]

I think it is fine for now, but we should probably update xtask at some point to run cargo udeps for this as well.

[github-actions]

Reproducibility Index:

2ed61030604ebf6ce86489399886cbf4422c623c4c4ce81e621792a01b979e99  ./target/x86_64-unknown-linux-musl/release/oak_functions_loader_base
d83458c923437b35df01f3d8a72dc55ae4d32a6eb9f91626356893c519d6e3b0  ./target/x86_64-unknown-linux-musl/release/oak_functions_loader_unsafe

Reproducibility Index diff:

diff --git a/reproducibility_index b/reproducibility_index
index 728a5d2..162f99d 100644
--- a/reproducibility_index
+++ b/reproducibility_index
@@ -1,2 +1,2 @@
-8a7d039cbdea7691dee83744f996b941eb3f174a9eb9376c5b8e06c49fb38f21  ./target/x86_64-unknown-linux-musl/release/oak_functions_loader_base
-9142c165d3c22874be1293d4f1c7f15341d18cc363f79f77931b95668d5c98db  ./target/x86_64-unknown-linux-musl/release/oak_functions_loader_unsafe
+2ed61030604ebf6ce86489399886cbf4422c623c4c4ce81e621792a01b979e99  ./target/x86_64-unknown-linux-musl/release/oak_functions_loader_base
+d83458c923437b35df01f3d8a72dc55ae4d32a6eb9f91626356893c519d6e3b0  ./target/x86_64-unknown-linux-musl/release/oak_functions_loader_unsafe