kernel-modules: increase SDHCI driver inclusion

kernel-modules: increase SDHCI driver inclusion

The sdhci-pci module is currently not being included in the initramfs,
even though other sdhci modules are. This breaks boot on systems that
rely on this driver to access the root filesystem.

Instead of looking for modules that use sdhci_pltfm_init, look for
sdhci_add_host. I checked 3.18 kernel sources, and this change
does not remove any of the previously-matched SDHCI drivers.
It should result in the addition of sdhci-pci, sdhci-s3c, sdhci-spear
and sdhci-acpi.