sdhci: add optional quirk property to disable card insertion/removal interrupts

This is needed for a quirk of the Raspberry Pi (bcm2835/6) MMC
controller, where the card insert bit is documented as unimplemented
(always reads zero, doesn't generate interrupts) but is in fact
observed on hardware as set at power on, but is cleared (and remains
clear) on subsequent controller resets.

Signed-off-by: Andrew Baumann <Andrew.Baumann@microsoft.com>
Reviewed-by: Peter Crosthwaite <crosthwaite.peter@gmail.com>
Message-id: 1450738069-18664-4-git-send-email-Andrew.Baumann@microsoft.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>