drivers: disk: Decouple SDMMC and MMC Kconfigs

MMC was using SDMMC kconfigs to build disk driver.
This is incorrect, MMC and SDMMC should not be sharing
Kconfigs. Split the drivers/disk/Kconfig.sdmmc into
drivers/disk/Kconfig.mmc and drivers/disk/Kconfig.sdmmc.

Also update disk tests to account for new MMC Kconfigs.

Signed-off-by: Declan Snyder <declan.snyder@nxp.com>