Bus_SPI: initialize spi_bus_config_t::dma_burst_size for ESP-IDF 6.1

[ainyan03]

Fixes #278.

ESP-IDF v6.1 added dma_burst_size to spi_bus_config_t. spi::init() seeds the struct with memset(&buscfg, ~0u, ...) so that every *_io_num defaults to -1, which leaves the new field at 0xFFFFFFFF. On chips whose GDMA burst size is configurable the driver rejects that value, spi_bus_initialize() fails inside alloc_dma_chan(), and its error path then panics (LoadProhibited), so init() boot-loops.

This sets dma_burst_size = 0 (driver default) on v6.1 and later. The assignment is placed inside the existing #if defined (ESP_IDF_VERSION_VAL) block so that toolchains without esp_idf_version.h keep compiling.

Affected chips (from the v6.1 sources): ESP32-S3 / C5 / C61 / H4 (GDMA_LL_AHB_BURST_SIZE_ADJUSTABLE) and ESP32-P4 / S31 (SOC_AXI_GDMA_SUPPORTED). ESP32 / S2 have no GDMA, and C3 / C6 / C2 / H2 force the default burst size regardless of the requested value, so they were never affected.

Verification

A/B on hardware with ESP-IDF v6.1 (tag), M5GFX from develop vs. this branch:

Board	Chip	Without fix	With fix
StickS3	ESP32-S3	invalid max_data_burst_size: 4294967295 → panic loop	boots, display OK
CoreS3	ESP32-S3	same	boots, display OK
ToughC5	ESP32-C5	same	boots, display OK
Tab5	ESP32-P4	same (via spi::init on Port B, since the DSI panel path does not touch SPI)	spi::init OK, DSI display OK

• No behaviour change on earlier IDF versions (the field does not exist there); Arduino-ESP32 3.x (ESP-IDF 5.5) build checked.
• CI on the fork: Arduino / ESP-IDF build workflows green.