spi: Split transfers larger than max size

spi: Split transfers larger than max size

A couple of drivers call spi_split_transfers_maxsize() from their
->prepare_message() callbacks to split transfers which are too big for
them to handle.  Add support in the core to do this based on
->max_transfer_size() to avoid code duplication.

Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
Link: https://lore.kernel.org/r/20220927112117.77599-4-vincent.whitchurch@axis.com
Signed-off-by: Mark Brown <broonie@kernel.org>