Initial work for the mmc_disk driver

No read and write support for now. But we implement getting SD card
capacity. SDHC is not supported yet (it uses a different layout for the
CSD register which will be rejected by this version of the code)

Change-Id: Ife844a62f3846c0a780259e9a3a08195e2fd965e
Reviewed-on: https://review.haiku-os.org/c/haiku/+/1068
Reviewed-by: Jérôme Duval <jerome.duval@gmail.com>