Support for the Secure Digital protocol in the MMC layer.

A summary of the legal issues surrounding SD cards, as understood by yours
truly:

Members of the Secure Digital Association, hereafter SDA, are required to sign
a NDA[1] before given access to any specifications.  It has been speculated
that including an SD implementation would forbid these members to redistribute
Linux.  This is the basic problem with SD support so it is unclear if it even
is a problem since it has no effect on those of us that aren't members.

The SDA doesn't seem to enforce these rules though since the patches included
here are based on documentation made public by some of the members.  The most
complete specs[2] are actually released by Sandisk, one of the founding
companies of the SDA.

Because of this the NDA is considered a non-issue by most involved in the
discussions concerning these patches.  It might be that the SDA is only
interested in protecting the so called "secure" bits of SD, which so far
hasn't been found in any public spec.  (The card is split into two sections,
one "normal" and one "secure" which has an access scheme similar to TPM:s).

(As a side note, Microsoft is working to make things easier for us since they
want to be able to include the source code for a SD driver in one of their
development kits.  HP is making sure that the new NDA will allow a Linux
implementation.  So far only the SDIO specs have been opened up[3].  More will
hopefully follow.)

 [1] http://www.sdcard.org/membership/images/ippolicy.pdf
 [2] http://www.sandisk.com/pdf/oem/ProdManualSDCardv1.9.pdf
 [3] http://www.sdcard.org/sdio/Simplified%20SDIO%20Card%20Specification.pdf

This patch contains the central parts of the SD support.  If no MMC cards are
found on a bus then the MMC layer proceeds looking for SD cards.  Helper
functions are extended to handle the special needs of SD cards.
Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>