sm8x50: Enable booting from mmc-sdcard am: ef6d03d767 am: 7b7bc7e0cc

Original change: https://android-review.googlesource.com/c/device/linaro/dragonboard/+/3115345

Change-Id: Id0522190302faf2428e3277a64bcb8e598e4f292
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>