Split tdx feature into tdcall and tdvmcall features as tdvmcall usage may be optional for some use cases

[sgrams]

No functional changes to existing build.
Now:

• tdx-tdcall/src/tdx.rs is split into two files: tdx-tdcall/src/tdcall.rs and tdx-tdcall/src/tdvmcall.rs.
• tdx-tdcall: tdx feature is split into tdcall and tdvmcall
• all dependent libraries start using tdcall and tdvmcall features instead of tdx feature
• td-shim/Cargo.toml and td-payload/Cargo.toml still provide tdx feature for backward compatibility, and it does include both tdcall and tdvmcall features.

[jyao1]

I am worried on the compatibility, since there is code change. For example:

-        1 => tdx::tdvmcall_io_read_8(port) as u32,
-        2 => tdx::tdvmcall_io_read_16(port) as u32,
-        4 => tdx::tdvmcall_io_read_32(port),
+        1 => tdvmcall::io_read_8(port) as u32,
+        2 => tdvmcall::io_read_16(port) as u32,
+        4 => tdvmcall::io_read_32(port),

How do you guarantee the consumer is NOT impacted?

Also, please describe the purpose of this change, not just what the patch does.

[sgrams]

This change is to allow consumers of TD-Shim to build it without support for TDVMCALLs.
We require this change in TEE-IO Provision Agent (TPA TD).

With this approach consumer must adapt, and a code change is required.
tdx::tdcall_* usage must be renamed to tdcall::*
tdx::tdvmcall_* usage must be renamed to tdvmcall::*
Imports are also affected.

[jyao1]

That introduces too many changes.

I think an easy way can be: just add [no-tdvmcall] to meet the need.

[sgrams]

I'll prepare a change with no-tdvmcall feature.