spi: mt65xx: Add dma max segment size declaration

Add spi dma max segment size declaration according to spi
hardware capability, instead of 64KB by system default
setting, to improve bus bandwidth for mass data transmission.

Signed-off-by: zhichao.liu <zhichao.liu@mediatek.com>
Link: https://lore.kernel.org/r/20220927083248.25404-1-zhichao.liu@mediatek.com


Signed-off-by: Mark Brown <broonie@kernel.org>