mmc: atmel-mci: move atmel-mci-regs.h content in atmel-mci.c

atmel-mci-regs.h is only included in atmel-mci.c so move its content in
the driver and do some cleanup in these definitions to remove checkpatch
errors.

Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>