spi: introduce max_message_size hook in spi_master

Recently a maximum transfer size was was introduced in struct spi_master.
However there are also spi controllers with a maximum message size, e.g.
fsl-espi has a max message size of 64KB.
Introduce a hook max_message_size to deal with such limitations.

Also make sure that spi_max_transfer_size doesn't return greater values
than spi_max_message_size, even if hook max_transfer_size is not set.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>