ESP32C6: Basic ESP32-C6 `example_build`

[alieissa-commits]

Goal: Get a bare-bones ThreadX kernel running on your physical ESP32-C6 development board

Deliver:

• Minimal directory under ports/risc-v32/gnu/example_build/esp32c6
• ESP32-C6 startup, linker script, vectors, PLIC, console, and SYSTIMER files contained under the example directory.
• ELF, map file, application image, and flash instructions.
• ThreadX tx_application_define validation application.
• Context switching and preemption.
• 100 Hz kernel tick.
• Console, reset, GPIO, and a peripheral interrupt.

Exit Criterion: Sustained thread, timer, queue, mutex, and interrupt stress without context corruption or timing stalls on an ESP32-C6 board. The example has no NetX Duo, Wi-Fi, or SampleX application dependency.