Add a means of getting platform data for the SDHCI PCI
devices. The data is stored against the slot not the
device in order to support multi-slot devices.
The data allows platform-specific setup (such as getting
GPIO numbers from firmware or setting up wl12xx for SDIO)
to be done in platform support files instead of the
sdhci-pci driver.
Signed-off-by: Adrian Hunter
Signed-off-by: Chris Ball