au1xmmc: remove db1200 board code, rewrite probe.

Remove the DB1200 board-specific functions (card present, read-only,
activity LED methods) and instead add platform data which is passed
to the driver.  This also allows for platforms to implement other
carddetect schemes (e.g. dedicated irq) without having to pollute the
driver code.  The poll timer (used for pb1200) is kept for compatibility.

With the board-specific stuff gone, the driver's ->probe() code can be
cleaned up considerably.

Signed-off-by: Manuel Lauss <mano@roarinelk.homelinux.net>
Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>