Heads up: new SD controller driver for Raspberry Pi in -current

[Jared McNeill <jmcneill%invisible.ca@localhost>]

Hi folks --

I've added a new driver for the Raspberry Pi's SD card controller to 
-current. The BCM283x family includes two SD card controllers; one is an 
Arasan SDHCI compliant controller (sdhc(4) driver) and another internal SD 
HOST controller (the new sdhost(4) driver).

Up until now, we have been using the SDHCI controller to drive the SD 
card slot. The SD HOST controller cannot do SDIO, so using it for the SD 
card slot will allow us to free up the SDHCI controller for use with the 
Wi-Fi chip on the Pi 3 and Zero W boards.

If you have any issues with the new driver, please report them to 
port-arm@. Removing the "sdhost" driver from your kernel will revert to 
the old behavior of using "sdhc" for SD cards.

Cheers,
Jared