MMC: MMCI: allow GPIOs to be passed

Add and initialize the gpio_wp and gpio_cd members.  We need to
ensure that all users are covered, because GPIO 0 may be valid.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Acked-by: Linus Walleij <linus.walleij@stericsson.com>