mmc: core SDIO suspend/resume support

Currently, all SDIO cards are virtually removed upon a suspend, and
completely reprobed upon a resume.  This adds the suspend and resume
methods to the SDIO bus driver so to be able to dispatch those events to
the actual SDIO function drivers for real suspend/resume instead.

All active functions on a card must have a driver with both a suspend and
a resume method though.  Failing that, we fall back to the current
behavior of simply "removing" the card when suspending.

When resuming, we make sure the same card is still inserted by comparing
the vendor and product IDs.  If there is a mismatch, or if there is simply
no card anymore in the slot, then the previous card is "removed" and the
new card is detected.  This is further enhanced with the next patch.

[akpm@linux-foundation.org: fix warnings]
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>