MMC: OMAP: Supporting MMC multislot structures for TI OMAP H2 board

Proposes the new board-h2-mmc.c file to handle all the mmc
specific code for multislot support.

Signed-off-by: Felipe Balbi <felipe.lima@indt.org.br>
Signed-off-by: Anderson Briglia <anderson.briglia@indt.org.br>
Signed-off-by: Carlos Eduardo Aguiar <carlos.aguiar@indt.org.br>
Signed-off-by: David Cohen <david.cohen@indt.org.br>
Signed-off-by: Eduardo Valentin <eduardo.valentin@indt.org.br>
Signed-off-by: Tony Lindgren <tony@atomide.com>