spi: stm32: add STM32F7 support

The STM32F7 SPI peripheral is similar to the STM32F4, except it allows
arbitrary word lengths between 4 and 16 bits, and has a small 32-bit
FIFO that allows two 8-bit or smaller words to be transferred with a
single 16-bit read/write.

Signed-off-by: Ben Wolsieffer <ben.wolsieffer@hefring.com>
Link: https://lore.kernel.org/r/20231102193722.3042245-5-ben.wolsieffer@hefring.com


Signed-off-by: Mark Brown <broonie@kernel.org>