sm8x50: Enable booting from mmc-sdcard am: ef6d03d767

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

Change-Id: Ic37dc14826028418a6657499359121dcf44f7689
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>