mmc: Implement card detection.

Check for card detect each time an MMC/SD device is initialized. If card
detection is not implemented, this code behaves as before and continues
assuming a card is present. If no card is detected, has_init is reset
for the MMC/SD device (to force initialization next time) and an error
is returned.

Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
Tested-by: Jason Liu <jason.hui@linaro.org>
diff --git a/drivers/mmc/arm_pl180_mmci.c b/drivers/mmc/arm_pl180_mmci.c
index e6467a2..09d443e 100644
--- a/drivers/mmc/arm_pl180_mmci.c
+++ b/drivers/mmc/arm_pl180_mmci.c
@@ -385,6 +385,7 @@
 	dev->send_cmd = host_request;
 	dev->set_ios = host_set_ios;
 	dev->init = mmc_host_reset;
+	dev->getcd = NULL;
 	dev->host_caps = 0;
 	dev->voltages = VOLTAGE_WINDOW_MMC;
 	dev->f_min = dev->clock;