mmc: add Faraday FTSDC021 SDHCI controller support

Faraday FTSDC021 is a controller which is compliant with
SDHCI v3.0, SDIO v2.0 and MMC v4.3.

However this driver is only verified with SD memory cards.

Signed-off-by: Kuo-Jung Su <dantesu@faraday-tech.com>
Acked-by: Pantelis Antoniou <panto@antoniou-consulting.com>
CC: Andy Fleming <afleming@gmail.com>