armv7

So far, even if CONFIG_MMC was not enabled the board code was trying to use
the MMC-related functions, resulting in linker errors.

Protect those calls by an ifdef.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>