sdhci-of: don't hard-code inverted write-protect quirk

MPC85xx SOCs have normal write-protect state reporting, so we shouldn't
hard-code the quirk.

Instead, look for "sdhci,wp-inverted" property, plus check for
mpc837x_{rdb,mds} machines since older device trees don't specify the new
property.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Cc: Pierre Ossman <pierre@ossman.eu>
Cc: Kumar Gala <galak@kernel.crashing.org>
Cc: David Vrabel <david.vrabel@csr.com>
Cc: Ben Dooks <ben@fluff.org>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: <linux-mmc@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>