MFC: r234524

MFC: r234524

o Fixes:
  - When switching to 4-bit operation, send a SET_CLR_CARD_DETECT command
    to disconnect the card-detect pull-up resistor from the DAT3 line before
    sending the SET_BUS_WIDTH command.
  - Add the missing "reserved" zero entry to the mantissa table used to
    decode various CSD fields. This was causing SD cards to report that they
    could run at 30 MHz instead of the maximum 25 MHz mandated in the spec.
o Enhancements:
  - At the MMC layer, format various info from the CID into a string that
    uniquely identifies the card instance (manufacturer number, serial
    number, product name and revision, etc). Export it as an instance
    variable.
  - At the MMCSD layer, display the formatted card ID string, and also
    report the clock speed of the hardware (not the card's max speed), and
    the number of bits and number of blocks per transfer. It comes out like
    this now:
    mmcsd0: 968MB <SD SD01G 8.0 SN 276886905 MFG 08/2008 by 3 SD> at mmc0
    22.5MHz/4bit/128-block
o Use DEVMETHOD_END.
o Use NULL instead of 0 for pointers.

PR:		156496
Submitted by:	Ian Lepore

git-svn-id: svn://svn.freebsd.org/base/stable/9@236089 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f