mmc: ftsdc021_sdhci: remove the ftsdc021_sdhci.c

ftsdc021_sdhci.c is dead file.
There is no reason to maintain this host controller.
Removes the entire ftsdc021_sdhci.c.

Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Reviewed-by: Tom Rini <trini@konsulko.com>