spi_mcux_ecspi does not handle transfers with 32 bits.

[voltamund]

Describe the bug

Target platform: MIMX8MM6 Cortex M4
I can use the spi_mcux_ecspi driver for transfers where each SPI word is 8 bits. However, it fails if an SPI word is 32 bits.

zephyr/drivers/spi/spi_mcux_ecspi.c

Line 96 in 6dce233

transfer.dataSize = data->dfs;

for 8 bits dfs will be 1 and the transfers are handled correctly. For 32 bits dfs will be 4 and the transfers will fail.
With the current driver implementation transfer.dataSize should always be 1.

Expected behavior

The spi_mcux_ecspi driver should support transfer sizes up to 32 bits.

Environment (please complete the following information):

• OS: Linux
• Toolchain: zephyr-sdk-0.16.8
• Zephyr Version 3.7.0

[pdgendt]

This driver can be improved a lot, especially if DMA would be added, feel free to send a PR for the 32 bit support.