mmc: atmel-mci: move mach header to platform_data

Move the mach header that can come either from arm/mach-at91 or avr32 to
platform_data to be able to switch the AT91 platforms to multiplatform.

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
[Ulf: Fixed compile error]