mtd: rawnand: stm32_fmc2: use dma_get_slave_caps to get DMA max burst

Use dma_get_slave_caps API to get the max burst size of a DMA channel.

For MP1 SoCs, MDMA is used and the max burst size is 128.
For MP25 SoC, DMA3 is used and the max burst size is 64.

Signed-off-by: Christophe Kerello <christophe.kerello@foss.st.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20240219140505.85794-3-christophe.kerello@foss.st.com