sdhci: Add sysctl to report quirks on the slot

[jhibbits]

Summary

It can be useful to see what quirks are applied on an SDHCI slot.

Obtained from: Juniper Networks, Inc.

[imp]

sys/dev/sdhci/sdhci.c

1148

I'd think this should be under the slot specific node. Why is it here instead of there? dev == slot->bus here, I think and it seems like it would be better add it under slotX, no? And if not in the slot, then I'd think we should set it elsewhere.

Otherwise, it looks fine.

[jhibbits]

Put it in the right place.