sdhci-s3c: add support for new card detection methods

sdhci-s3c: add support for new card detection methods

On some Samsung SoCs not all SDHCI controllers have card detect (CD) line.
 For some embedded designs it is not even needed, because ususally the
device (like SDIO flash memory or wifi controller) is permanently wired to
the controller.  There are also systems which have a card detect line
connected to some of the external interrupt lines or the presence of the
card depends on some other actions (like enabling a power regulator).

This patch adds support for all these cases.  The following card detection
methods are possible:

1. internal sdhci host card detect line
2. external event
3. external gpio interrupt
4. no card detect line, controller will poll for the card
5. no card detect line, card is permanently wired to the controller
(once detected host won't poll it any more)

By default, all existing code would use method #1, what is compatible with
the previous version of the driver.

In case of external event, two callbacks must be provided in platdata:
ext_cd_init and ext_cd_cleanup.  Both of them get a callback to a function
that notifies the s3c-sdhci host contoller as their argument.  That
callback function should be called from the even dispatcher to let host
notice the card insertion/removal.

In case of external gpio interrupt, a gpio pin number must be provided in
platdata (ext_cd_gpio parameter), as well as the information about the
polarity of that gpio pin (ext_cd_gpio_invert).  By default
(ext_cd_gpio_invert == 0) gpio value 0 means 'card has been removed', but
this can be changed to 'card has been removed' when ext_cd_gpio_invert ==
1.

This patch adds all required changes to sdhci-s3c driver.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.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>