spi: Updates for v4.8 Quite a lot of cleanup and maintainence work going on this release in various drivers, and also a fix for a nasty locking issue in the core: - A fix for locking issues when external drivers explicitly locked the bus with spi_bus_lock() - we were using the same lock to both control access to the physical bus in multi-threaded I/O operations and exclude multiple callers. Confusion between these two caused us to have scenarios where we were dropping locks. These are fixed by splitting into two separate locks like should have been done originally, making everything much clearer and correct. - Support for DMA in spi_flash_read(). - Support for instantiating spidev on ACPI systems, including some test devices used in Windows validation. - Use of the core DMA mapping functionality in the McSPI driver. - Start of support for ThunderX SPI controllers, involving a very big set of changes to the Cavium driver. - Support for Braswell, Exynos 5433, Kaby Lake, Merrifield, RK3036, RK3228, RK3368 controllers.