Among other things this causes startup errors to kick in the
fallback "reset harder" logic during server startup. Comments
are also updated a bit, explaining what the various error paths
signify (in at least my observation).
There's one class of validation error that we can still plausibly
ignore: when wrong IDCODE values are observed.
This change seems to have helped make an OMAP5912 behave much
more reliably. There's still some post-reset flakiness, but
it's unrelated to scan verification.
Signed-off-by: David Brownell <email@example.com>