Fix ESP32-S3 GPIO_PIN_COUNT compatibility

[fresh3nough]

Summary

• define GPIO_PIN_COUNT when building against newer ESP32-S3 SDKs that only provide SOC_GPIO_PIN_COUNT, before including rtc_io.h.

Reproduction

1. Use PlatformIO with an ESP32-S3 board (e.g., heltec_wifi_kit_32_V3).
2. Build a sketch that compiles Heltec SX1262 radio sources (RADIO_CHIP_SX1262) which include driver/rtc_io.h.
3. On modern Arduino-ESP32/ESP-IDF, the build fails with 'GPIO_PIN_COUNT' undeclared in rtc_io.h.

Tests

• Attempted: python3 -m platformio run -d /tmp/heltec_pio_211
  • Blocked by existing src/driver/sx126x.h parse error (stray */ after LORA_MAC_PUBLIC_SYNCWORD).

Co-Authored-By: Warp agent@warp.dev

[caveman99]

a note to maintainers - do NOT merge this. Agentic Bot that doesn't take NO for an answer.