ARM: h1940: Implement mmc_power function

This patch implements h1940-specific set_power callback for
s3cmci driver, so card power can be disabled when card is not inserted
or before suspend. Without this patch PDA consumes power in suspend when
card is inserted.

Signed-off-by: Vasily Khoruzhick <anarsoul@gmail.com>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>