mmc: dw_mmc: Remove old card detect infrastructure

The dw_mmc driver had a bunch of code that ran whenever a card was
ejected and inserted.  However, this code was old and crufty and
should be removed.  Some evidence that it's really not needed:

1. Is is supposed to be legal to use 'cd-gpio' on dw_mmc instead of
   using the built-in card detect mechanism.  The 'cd-gpio' code
   doesn't run any of the crufty old code but yet still works.

2. While looking at this, I realized that my old change (369ac861 mmc:
   dw_mmc: don't queue up a card detect at slot startup) actually
   castrated the old code a little bit already and nobody noticed.
   Specifically "last_detect_state" was left as 0 at bootup.  That
   means that on the first card removal none of the crufty code ran.

3. I can run "while true; do dd if=/dev/mmcblk1 of=/dev/null; done"
   while ejecting and inserting an SD Card and the world doesn't
   explode.

If some of the crufty old code is actually needed, we should justify
it and also put it in some place where it will be run even with
"cd-gpio".

Note that in my case I'm using the "cd-gpio" mechanism but for various
reasons the hardware triggers a dw_mmc "card detect" at bootup.  That
was actually causing a real bug.  The card detect workqueue was
running while the system was trying to enumerate the card.  The
"present != slot->last_detect_state" triggered and we were doing all
kinds of crazy stuff and messing up enumeration.  The new mechanism of
just asking the core to check the card is much safer and then the
bogus interrupt doesn't hurt.

Signed-off-by: Doug Anderson <dianders@chromium.org>
Tested-by: Jaehoon Chung <jh80.chung@samsung.com>
Acked-by: Jaehoon Chung <jh80.chung@samsung.com>
Tested-by: alim.akhtar <alim.akhtar@samsung.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>