thinknode_m9: pick GPS enable polarity from the board revision

The GPS enable pin (GPIO11) is active-LOW on the original ThinkNode-M9 but
active-HIGH on the newer revision (keyboard controller at 0x6D, e.g. Elecrow's
Meshtastic SKU LMM15409D2). Driven LOW on those units the GPS never gets a
fix: on one unit, same spot, 0 satellites with EN active-LOW vs 15 with
active-HIGH, and 34 after 20 minutes outdoors with the GPS toggled off and on
again from the UI. Meshtastic's ELECROW-ThinkNode-M9 variant makes the same
split, keyed on the same keyboard address (m9Version > 1 ? HIGH : LOW), and
Elecrow engineers have confirmed the split.

WadaNmeaLocationProvider: keep the enable level in a member that defaults to
the compile-time GPS_EN_ACTIVE, add setEnActive() to override it at runtime
(re-driving the pin so a running GPS stays on), and an optional
setPostEnableHook() run at the end of begin(). Every other board is unaffected.

thinknode_m9: m9KeyboardAddr() and a one-shot found-callback on the keyboard
driver; target.cpp uses it, when the controller is at 0x6D, to call
gps.setEnActive(true) and to register a GPIO10 wake pulse (50 ms, HIGH 5 ms,
LOW, 50 ms) after enabling, as Elecrow engineers confirmed. Any other address
keeps the existing default (LOW, no pulse), so the 0x6C path is unchanged; it
is not tested here, no 0x6C unit was available.

Depends on the keyboard 0x6D probe change.

Signed-off-by: Pratik Patel <Pratik@MakerNova.io>

variants/thinknode_m9/target.cpp

@@ -56,6 +56,35 @@ DISPLAY_CLASS display(&board.periph_power);
 #define LORA_CR 5
 #endif
 
+#if defined(HAS_M9_KEYBOARD)
+// The keyboard controller's I2C address identifies the board hardware revision:
+// units whose keyboard answers at 0x6D carry the newer GPS wiring, whose enable pin
+// is active HIGH (same split Meshtastic and Elecrow's firmware make), followed by a
+// short wake pulse on GPIO10. 0x6C boards keep the compile-time default
+// (PIN_GPS_EN_ACTIVE, LOW) and no pulse.
+// Elecrow's own firmware pulses GPIO10 (the module's ON_OFF/wake line) after
+// driving EN active on these units: 50 ms, HIGH for 5 ms, then 50 ms settle.
+static void m9GpsWakePulse() {
+  pinMode(10, OUTPUT);
+  delay(50);
+  digitalWrite(10, HIGH);
+  delay(5);
+  digitalWrite(10, LOW);
+  delay(50);
+}
+
+static void m9OnKeyboardFound(uint8_t addr) {
+  if (addr == 0x6D) {
+    gps.setEnActive(true);
+    gps.setPostEnableHook(m9GpsWakePulse);
+    if (gps.isEnabled()) m9GpsWakePulse();   // GPS was already powered before the keyboard was found
+    Serial.println("M9 GPS: enable pin active HIGH (keyboard at 0x6D)");
+  } else {
+    Serial.printf("M9 GPS: enable pin active level unchanged (keyboard at 0x%02X)\n", addr);
+  }
+}
+#endif
+
 bool radio_init() {
   fallback_clock.begin();
   // peripheral I2C bus (7/6) — RTC PCF8563 @ 0x51, brought up by
@@ -65,6 +94,7 @@ bool radio_init() {
   if (hw_rtc.adopted()) rtc_clock.noteHardwareTime();
 
 #if defined(HAS_M9_KEYBOARD)
+  m9KeyboardSetFoundCallback(m9OnKeyboardFound);
   m9KeyboardBegin(); // own bus, Wire1 (20/21) — no contention with Wire
 #endif
 #if defined(HAS_M9_COMPASS)