mmc-twl4030 voltage cleanup

Correct twl4030 MMC power switching:  fix voltage ranges reported
for each slot, and handle them fully.

 Lies corrected:
  - MMC-1 doesn't support the 2.6-2.7 Volt range
  - MMC-2 can't normally support anything except 1.8V
 Omissions corrected
  - MMC-1 *does* handle the 2.8-2.9 Volt range
  - MMC-2 can handle 2.5-3.2 Volt cards, given a transceiver

Add transciever support for MMC-2; enable it for Overo and Pandora.
(Depends on something else to have set up pinmuxing for control
signals instead of as MMC2_DAT4..7 pins.)

Also shrink twl4030_hsmmc_info a smidgeon ... padding is all gone.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Tony Lindgren <tony@atomide.com>