ARM: OMAP: Clean-up MMC device init

Clean-up MMC device init:

- Initialize devices in mach-omap1/devices.c and mach-omap2/devices.c
  instead of plat-omap/devices.c

- Remove old struct omap_mmc_config, use struct omap_mmc_platform_data instead

Note that this removes the second omap-hsmmc controller init for overo.
This needs to be fixed properly by changing hsmmc_init() to accept
board specific struct omap_mmc_platform_data.

Signed-off-by: Tony Lindgren <tony@atomide.com>