Update bootloader environment for BPi-R3 and BPi-R64 to adapt to new
device tree overlay mechanism now that support for multiple device
tree overlays has been added.
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
(cherry picked from commit ec50d2d366fecb6f4bac2ae9d5cfa4aba9cf7bbc)