base: Minor Cargo.toml changes for ChromeOS support.
base: Minor Cargo.toml changes for ChromeOS support.

Add 'provided by ebuild' in necessary places to install crosvm's base
crate on ChromeOS as crosvm_base. Also fix dependency ordering and add a
missing version attribute.

BUG=b:229016539
TEST=FEATURES=test emerge-${BOARD} crosvm_base

Change-Id: Ie09e16819e7e27664b5897afd8c6a40e19cc87ec
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/3703158
Auto-Submit: Allen Webb <880184b418addffb87cd9c8e8e882ca6764ac96b@google.com>
Reviewed-by: Dennis Kempin <cd09796fb571bec2782819dbfd33307f65b1c778@google.com>
Commit-Queue: Dennis Kempin <cd09796fb571bec2782819dbfd33307f65b1c778@google.com>
Tested-by: Dennis Kempin <cd09796fb571bec2782819dbfd33307f65b1c778@google.com>

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