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`make flash` will install the firmware onto a board in BOOTROM mode.
This target requires `rkdeveloptool` to be in the `$PATH` and for
`MiniLoaderAll.bin` to be in the build directory.
Signed-off-by: Grant Likely <grant.likely@arm.com>

The makefile for all three platforms is largely identical. Consolidate
all three into a single Makefile that is used for all, and only hold the
differences in the per platform makefile.
Signed-off-by: Grant Likely <grant.likely@arm.com>

Signed-off-by: Grant Likely <grant.likely@arm.com>

Don't reset the U-Boot source tree and don't apply any patches to the
tree so that the version of u-boot is entirely controlled by the
manifest file instead of resetting to a specific tag.

Also removes the DFU_ALT_INFO config from the Leez for now until the DFU
patch gets applied to a U-Boot git repo that can be referenced that
already includes the patch
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

Many Linux distros already provide an aarch64 cross compile toolchain.
In toolchain.mk, if the toolchain is already in the path then use that
instead of a separate downloaded version.
Signed-off-by: Grant Likely <grant.likely@arm.com>