[MMC] sdhci: support controller specific quirks

As some specific controllers will have bugs, we need a way to map special
behaviour to certain hardware.

Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>