fix(nrf52): enable USB/charge detection on Seeed Wio Tracker L1 (#10941)

isCharging()/getHasUSB() were hard-compiled to always return false on
this board: the nrfx_power_usbstatus_get() block in Power.cpp that
derives them is gated behind #ifdef NRF_APM, and this board's variant.h
never defined it - unlike tracker-t1000-e and wio-tracker-wm1110, which
do. Confirmed on hardware: before this change, `Battery: usbPower=0,
isCharging=0` regardless of actual USB/charge state; after, `usbPower=1,
isCharging=1` while genuinely on USB power with a battery attached.

Same underlying gap as #4367, fixed for tracker-t1000-e and
wio-tracker-wm1110 in #4376 (which also fixed a deeper bug where
PowerStatus notifications were gated behind a battery-level null check -
that part is already fixed generically in Power.cpp today, so this board
only needed the define). Looks like a simple oversight from when this
board was added, since it's newer than the two boards #4376 touched.

Assisted-by: Claude Sonnet 5 <noreply@anthropic.com>

Signed-off-by: Andrew Yong <me@ndoo.sg>

variants/nrf52840/seeed_wio_tracker_L1/variant.h

@@ -112,6 +112,8 @@ static const uint8_t SCL = PIN_WIRE_SCL;
 #define ADC_MULTIPLIER 2.0
 #define BATTERY_PIN PIN_VBAT // PIN_A7
 #define AREF_VOLTAGE 3.6
+// We rely on the nrf52840 USB controller to tell us if we are hooked to a power supply
+#define NRF_APM
 // ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
 //  GPS L76KB
 // ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━