spi: core: Validate length of the transfers in message

SPI transfer length should be multiple of SPI word size,
where SPI word size should be power-of-two multiple

Signed-off-by: Ivan T. Ivanov <iivanov@mm-sol.com>
Signed-off-by: Mark Brown <broonie@linaro.org>
(cherry picked from commit 4d94bd21)
(cherry picked from commit 591b5303f19da193ca20d3434c25797dd8b24b08)