plat/st: do not keep mmc_device_info in stack

Create a dedicated static struct mmc_device_info mmc_info mmc_info
instead of having this in stack.
A boot issue has been seen on some platform when applying patch [1].

 [1] 13f3c5166f1 ("mmc:prevent accessing to the released space in case of wrong usage")

Signed-off-by: Yann Gautier <yann.gautier@foss.st.com>
Change-Id: I73a079715253699d903721c865d6470d58f6bd30
1 file changed