uboot-phytec

mmc: make <mmc.h> self-contained

This header uses bd_t without including its definition.

Change it to (struct bd_info), and add the forward declaration
to specify it as a structure.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>