spi: spi-mt65xx: Use threaded interrupt for non-SPIMEM transfer

spi: spi-mt65xx: Use threaded interrupt for non-SPIMEM transfer

In order to avoid blocking for an excessive amount of time, eventually
impacting on system responsiveness, interrupt handlers should finish
executing in as little time as possible.

Use threaded interrupt and move the SPI transfer handling (both
CPU and DMA) for the non-spimem case to an interrupt thread instead.

For SPI-MEM (IPM) controllers, handling is kept in the blocking
interrupt as it simply consists in signalling completion.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://patch.msgid.link/20240726114721.142196-1-angelogioacchino.delregno@collabora.com
Signed-off-by: Mark Brown <broonie@kernel.org>