sdhci: add support for the SysKonnect CardBus2SDIO adapter

This is still in use especially to develop SDIO device drivers on laptop
machines which are lacking SDIO slots.  This adapter supports SDIO cards
only due to lack of 136-bit response capability.

Signed-off-by: Nicolas Pitre <nico@marvell.com>
Cc: <linux-mmc@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>