docs: Generate API docs only for first-party crates
docs: Generate API docs only for first-party crates

Pass `--workspace` and `--no-deps` as cargo-doc's arguements.
As a result:
* it won't generate API docs for third-party crates
* it'll generate API docs for our first crates that are not used by the
  minimal crosvm build. (e.g. qcow_utils, libvda, etc)

BUG=none
TEST=test on personal GitHub

Change-Id: I8911eb7d830f1cda77d264c1dc19ff948cfa4768
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/3578146
Reviewed-by: Dennis Kempin <cd09796fb571bec2782819dbfd33307f65b1c778@google.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Commit-Queue: Keiichi Watanabe <815e4e8f7c92a23424d7c3f51ead622bcedbc720@chromium.org>

google/crosvm,google/crosvm,google/crosvm,google/crosvm