spi: Updates for v4.18

Quite a busy release for SPI, mainly as a result of Boris Brezillon's
work on improving the integration with MTD for accelerated SPI flash
controllers.  He's added a new spi_mem interface which works a lot
better with general hardware and converted the users over to it, as a
result of this work we've got some MTD changes in here as well.

Other highlights include:

 - Lots of spring cleaning for the s3c64xx driver.
 - Removal of the bcm53xx, the hardware is also supported by the mspi
   driver but SoC naming had caused people to miss the duplication.
 - Conversion of the pxa2xx driver to use the standard message
   processing loop rather than open coding.
 - A bunch of improvements to the runtime PM of the OMAP McSPI driver.
Merge branch 'spi-4.17' into spi-4.18 for the merge window