Artemis Milestone 2c: xHCI controller bring-up wired, DoE CSV export off by default

xhci_bringup() (HC reset, DCBAA, Command/Event rings, RUN/STOP) was
uncommitted and referenced an XHCI_WAIT_FOR macro that was never defined,
breaking the build. Wired all four wait sites to the existing
xhci_wait_bit() helper instead, matching each register/bit/polarity
needed (halt-before-reset waits for HCH set; HCRST, CNR, and post-RUN
HCH waits all wait for their bit to clear).

Also flipped g_doe_log_enabled's default from 1 to 0 -- the per-tick
[HADES][DOE] CSV export was flooding every boot log and slowing
interactive verification for no reason during ordinary acceptance runs;
HB-ON still re-enables it at the REPL for anyone running an actual DoE
campaign.

Three-arch acceptance: amd64/aarch64/riscv64 all boot clean to ok>,
zero DoE rows in any log. aarch64 and riscv64 both exited cleanly via
BYE with no exception, confirming the earlier SMC->HVC PSCI fix still
holds. Logs and DoE CSV artifacts from this run included.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HZ8kNoTuP63pbQtro4qvrm

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