Bus_SPI: build the ESP32-C6 clock takeover with arduino-esp32 3.0 (ESP-IDF 5.1)

[ainyan03]

With arduino-esp32 3.0.x (ESP-IDF 5.1), an ESP32-C6 sketch fails to compile:

src/lgfx/v1/platforms/esp32/Bus_SPI.inl: error: 'PERIPH_RCC_ATOMIC' was not declared in this scope

The SPI clock takeover used on Arduino builds for C5 / C6 / C61 / P4 (temporarily selecting the 80 MHz GPSPI source when it gives a closer write clock) wraps its read-modify-write of the clock-source register in PERIPH_RCC_ATOMIC(), which ESP-IDF added in 5.2. C5 / C61 / P4 need arduino-esp32 3.1 or later and are not affected.

ESP-IDF 5.1 has no shared lock for that register (its own SPI driver writes the clock source without one). Where PERIPH_RCC_ATOMIC() is missing, the same block now runs inside a critical section of its own; with ESP-IDF 5.2 and later nothing changes.

Checks

• arduino-esp32 3.0.7 / ESP32-C6: compile error before, builds after. 3.1.x C6, P4, C5 still build.
• On two ESP32-C6 boards with an SPI display (arduino-esp32 3.0.7 and 3.1.3), with the write clock set to 27 MHz and the GPSPI source forced to XTAL beforehand: the source is XTAL before a transaction, PLL_F80M during it and XTAL again after (40 / 80 / 40 MHz), and a full-screen write reads back identical.