docs(rock5b): note 40-pin header has no power-on/wake-up signal

[tzz-radxa]

Why

A customer (ROCK 5B+ V1.2, 2026-09-12 support request) wants to implement an external hardware power-on / wake-up using only the 40-pin header (to avoid soldering wires onto the on-board PWR button). The current page documents the full 40-pin pinout but never says whether a power-on/wake-up control signal is available there, so users keep hunting for such a pin (and some even suspect the released schematic is incomplete).

What was verified

Checked against the officially released schematics:

• ROCK 5B+ V1.2 schematic (radxa_rock5bp_v1.2_schematic.pdf, 33 pages): sheet 29 CONNECT 40pin carries only 5V / 3V3 / GND / GPIO / SPI / I2C / UART / I2S / RTC nets.
• PWRON / PWRON_L appear only on the PMIC sheet (sheet 31 Power-PMIC_RK806-1) in the whole document — it is not routed to the 40-pin connector.
• ROCK 5B V1.45 schematic (radxa_rock_5b_v1450_schematic.pdf): PWRON likewise appears only on the PMIC sheet (page 22), not on the 40-pin page.

Changes

Add a short :::note right after the 40-pin GPIO pinout in rock5/rock5b/hardware-design/hardware-interface.md (zh + en), stating that:

• the 40-pin header exposes neither the PMIC PWRON power-on signal nor a wake-up signal;
• power-on / wake-up therefore cannot be triggered from a 40-pin pin;
• externally controlled power-on requires switching the 5V / USB-PD supply; applying 5V to the 40-pin 5V pins starts the board but is a supply power-up, not a pin-controlled trigger.

Notes

• Docs-only, bilingual pair (zh + en) updated in the same commit.
• No upstream issue for this; verified there is no existing issue/PR about the 40-pin power-on signal.
• pre-commit run --files passes (including the translation / bilingual guards); local PR guard reports ok=true (1 commit / 2 files / single scope docs/rock5/rock5b).