is MMC only and a uSD slot may be SD only.  However the MMC card scanning
logic checks for all card types one by one.

Add host capabilities to specify which card types can be used, and amend
the card scanning logic to skip scanning for those types which cannot be
used.
Signed-off-by: Matt Fleming <matt@console-pimps.org>
Acked-by: Matt Fleming <matt@console-pimps.org>
Cc: Ian Molton <ian@mnementh.co.uk>
Cc: "Roberto A. Foglietta" <roberto.foglietta@gmail.com>
Cc: Jarkko Lavinen <jarkko.lavinen@nokia.com>
Cc: Denis Karpov <ext-denis.2.karpov@nokia.com>
Cc: Pierre Ossman <pierre@ossman.eu>
Cc: Philip Langdale <philipl@overt.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>