spi: Updates for v4.6 Not the biggest set of changes for SPI but a bit of a pickup in activity on the core: - Support for memory mapped read from flash devices via a SPI controller. - The beginnings of a message rewriting framework in the core which should in time allow us to support transforming messages to work around the limits of controllers or optimise the performance for controllers transparently to calling drivers. - Updates to the PXA2xx, the main functional change being to improve the ACPI support. - A new driver for the Analog Devices AXI SPI engine.