spi: spl022: fix sleeping in interrupt context

spi: spl022: fix sleeping in interrupt context

Merge series from Nam Cao <namcao@linutronix.de>:

While running the spl022, I got the following warning:
BUG: sleeping function called from invalid context at drivers/spi/spi.c:1428

This is because between spi transfers, spi_transfer_delay_exec() (who
may sleep if the delay is >10us) is called in interrupt context. This is
a problem for anyone who runs this driver and need more than 10us delay.

Patch 1 adds an error reporting mechanism, needed by patch 2 who switch
to use the default spi_transfer_one_message(), which fix the problem.

The series is tested with polling transfer mode and interrupt transfer
mode. I can't test the DMA mode, so some help testing here is very
appreciated.