mmc: Add concept of an 'embedded' SDIO device.

This is required to support chips which use SDIO for signaling/
communication but do not implement the various card enumeration registers
as required for full SD / SDIO cards.

mmc: sdio: Fix bug where we're freeing the CIS tables we never allocated when using EMBEDDED_SDIO
mmc: Add max_blksize to embedded SDIO data

Signed-off-by: San Mehat <san@google.com>