Add command wrappers that simplify register access from SDIO
function drivers.
Signed-off-by: NPierre Ossman <drzeus@drzeus.cx>

Add the sdio bus type and basic device handling.
Signed-off-by: NPierre Ossman <drzeus@drzeus.cx>

Really basic init sequence for SDIO cards.
Signed-off-by: NPierre Ossman <drzeus@drzeus.cx>

Move basic host class device handling to its own file for clarity.
Signed-off-by: NPierre Ossman <drzeus@drzeus.cx>

Move bus operations to its own file for the sake of clarity. Also
delegate sysfs attributes to bus handlers in preparation for other
more exotic types.
Signed-off-by: NPierre Ossman <drzeus@drzeus.cx>

Delegate protocol handling to "bus handlers". This allows the core to
just handle the task of arbitrating the bus. Initialisation and
pampering of cards is now done by the different bus handlers.

This design also allows MMC and SD (and later SDIO) to be more cleanly
separated, allowing easier maintenance.
Signed-off-by: NPierre Ossman <drzeus@drzeus.cx>

Move protocol operations and definitions into their own files
in an effort to separate protocol handling and bus
arbitration more clearly.
Signed-off-by: NPierre Ossman <drzeus@drzeus.cx>

Create a "core" subdirectory to house the central bus handling
functions.
Signed-off-by: NPierre Ossman <drzeus@drzeus.cx>