cargo_embargo: use FIND_CRATE to locate Trusty modules

To support builds using the new monorepo for rust crates as well
as the old structure of one repo per crate under external/rust,
call FIND_CRATE for each library dependency rather than hardcoding
the path to the Trusty module.

Test: manually, build Trusty against monorepo for external crates
Change-Id: I3d7ccdcf150e6922166d0b1952f9f8e2d6a26ab9
1 file changed