Use the board detector for ESP32-P4 boards, rename PoE-P4 display output settings to Display Out

[ainyan03]

Summary

Leave ESP32-P4 board identification to the M5GFX board detector (m5stack/M5GFX#343), and rename the PoE-P4 display output settings to Display Out. Requires M5GFX with #343.

Changes

• Remove the P4 GPIO checks from _check_boardtype() (G32 high: Tab5, G0 high: Unit PoE-P4, otherwise Stamp-P4). User wiring can change both pins. M5GFX now confirms Unit PoE-P4 by its Ethernet PHY and reports Tab5 / Stamp-P4 candidates through getBoardCandidate().
• BOARD_ID 31 (CoreP4X) and 35 (Tab5X), set by board-specific firmware builds, now apply after cfg.fallback_board and before the detector's candidate. Otherwise the Stamp-P4 candidate that M5GFX reports for any unconfirmed P4 board would hide them.
• The P4 package default becomes Stamp-P4 / Stamp-P4X (by chip revision) instead of Tab5.
• Rename (separate commit): cfg.unit_poep4_display_out and cfg.external_display.unit_poep4_display_out replace the unit_poep4_hdmi names, which remain as deprecated members.
  • The two settings structures are separate members. If the deprecated one differs from its defaults it is used, with a warning.
  • Bit 9 of external_display_value is now unit_poep4_display_out; the deprecated flag moves to bit 10. Clearing either flag disables Display Out. A sketch that zeroes external_display_value and then sets only the deprecated flag no longer enables it; use the new name.
  • Examples use the new names.

Tested

• Stamp-P4 (chip v1.3), Tab5 (v1.0), Unit PoE-P4 (v1.3) with and without Display Out: M5.getBoard() = 150 / 22 / 148.
• Tab5 with the display setup forced to fail: M5.getBoard() = Tab5 through the candidate.
• Unit PoE-P4 + Display Out: attaches as a 1280x720 display with the new names; with the old names and 1920x1080@30 the old settings take effect, with deprecation warnings at build time and the runtime warning.
• Builds for the versions in the upstream CI (Arduino 2.0.17 / 3.x, ESP-IDF 4.4 – 6.1).
• Not tested: CoreP4X, Tab5X, Stamp-P4X (no hardware).

The depends on M5GFX in library.properties / library.json should be raised to the release that contains M5GFX#343; without it, a newer M5Unified with an older M5GFX silently skips Display Out.