beagle_x15: use prebuilt u-boot

In order to remove final arm32 gcc cross compiler, we need to be able to
build u-boot with Clang, but are facing:
Until that is fixed, move to a prebuilt binary for u-boot to unblock
removing old GCC as per:

Bug: 147296060
Test: lunch beagle_x15 && m && find $OUT -name MLO && \
  find $OUT -name u-boot.img
Signed-off-by: Nick Desaulniers <>
Change-Id: I848dba99e622e07560888a62d84bc9cb55f92050
3 files changed