drivers: mspi_dw: Add support for asynchronous transfers

Handling of asynchronous transfers uses the system workqueue,
hence they are not available when multithreading is disabled.

Also add missing dependency on multithreading in the
MSPI_DW_HANDLE_FIFOS_IN_SYSTEM_WORKQUEUE Kconfig option.

Signed-off-by: David Jewsbury <david.jewsbury@nordicsemi.no>
Signed-off-by: Andrzej Głąbek <andrzej.glabek@nordicsemi.no>
2 files changed