mmc: atmel-mci: Remove AVR32 bits from the driver

AVR32 is gone. Now it's time to clean up the driver by removing
leftovers that was used by AVR32 related code.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Ludovic Desroches <ludovic.desroches@microchip.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>