tegra2: Modify MMC driver to handle power and cd GPIOs

Pass the GPIO numbers for power and card detect to tegra2_mmc_init(), and
modify that function to perform all required GPIO initialization. This
removes the need for board files to perform these operations.

Move board_mmc_getcd() into tegra2_mmc.c now that the driver knows which
GPIOs to use.

Update affected call-sites in seaboard.c and harmony.c. Note that this
change should make all SD ports work on Harmony, since the required GPIO
setup is now being performed.

v4: Fix prototype of tegra2_mmc_init() in board.h to match driver change.
    Remove prototype of gpio_config_mmc() from board.h

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Cc: Andy Fleming <afleming@gmail.com>
Tested-by: Simon Glass <sjg@chromium.org>
Acked-by: Simon Glass <sjg@chromium.org>
Acked-by: Andy Fleming <afleming@freescale.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>