MFC r311734, r311735, r311951, r314071:

MFC r311734, r311735, r311951, r314071:

  Add new helper routines for sdhci bridge drivers that use gpio pins for
  card presence and write protect switch detection.

  Use the new sdhci_fdt_gpio helper functions to add full support for FDT
  gpio pins for detecting card insert/remove and write protect for ti_sdhci.

  Include sys/systm.h for use of bootverbose.

  Revert to ti_sdhci driver's historic behavior: assume an sd card is
  writable if the fdt data doesn't provide a gpio pin for reading the write
  protect switch and also doesn't contain a "wp-disable" property.