[bsp][esp32-c6] compile SPI when it is selected

[cms19859230182-lang]

Summary

• Selecting BSP_USING_SPI on ESP32-C6 now links the IDF SPI master. The default image still leaves SPI off.
• The shared ESP driver no longer falls through SPI modes, returns the transferred byte count, and takes the chip-select pin from SPI2_IOMUX_PIN_NUM_CS. C6 asks for SPI_DMA_DISABLED. Other chips keep SPI_DMA_CH_AUTO.
• spi_configure() returns -RT_EINVAL when configuration is null. The unused esp32_spi_init() call that passed NULL is gone.
• The peripheral table is unchanged. SPI stays unsupported. The GPIO7 to GPIO2 loopback was not run again.

Test plan

• ESP32-C6 with RT_USING_SPI, BSP_USING_SPI and BSP_USING_SPI2 added to rtconfig.h, RT_USING_ADC kept: scons exit 0. rtthread.bin is 466416 bytes. text is 371342. The link includes drv_spi, spi_common, spi_master, spi_hal and gdma.
• Those three lines removed, then scons again: exit 0. rtthread.bin is 445408 bytes. text is 340218. The link does not include drv_spi.
• Not flashed. The loopback was not run again.

[github-actions]

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[github-actions]

MemBrowse Memory Report

No memory changes detected for:

• esp32-c3