Update device numbers in tpu7x characteristics

[NuojCheng]

Description

Since for tpu7x the number of devices is equivalent with the number of cores (double of the number of chips), we should update the system characteristics accordingly. This PR also updates train_compile tests to verify.

Tests

train compile test

Checklist

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[richjames0]

lgtm