uboot-imx

MA-16457-1 avoid to try to access system partition

To enable dynamic partition feature, system partition will be a logic
parition in "super" partition, uboot can't access system partition
anymore.

In i.MX Android use case, only vbmeta partition is used to verify other
imags. boot and system are not used. so there is no need to access
system partition to get avb device info, remove system partition from
avb lib.

Now, standard Android will boot with ramdisk in boot.img, there is no
need to provide root info to kernel for standard Android. so only
Android Auto will provide this info.

Change-Id: I99a43eb8f7aa1dc635e3937c93266f881c9b3655
Signed-off-by: faqiang.zhu <faqiang.zhu@nxp.com>