u-boot: make initial environment binary image

u-boot: make initial environment binary image

Build the U-Boot initial environment binary image if
UBOOT_INITIAL_ENV_BINARY is set to "1". The environment partition size
(in bytes, hexadecimal or decimal) must be defined using
UBOOT_INITIAL_ENV_BINARY_SIZE.

If U-Boot environment redundancy is enabled,
UBOOT_INITIAL_ENV_BINARY_REDUND must be set to "1".

The resulting binary can be flashed using WIC at the environment offset,
overriding any existing environment if present, for example:

  part --source rawcopy --sourceparams="file=u-boot-initial-env-sd.bin" --ondisk sda --no-table --offset 4096

Signed-off-by: Pierre-Loup GOSSE <pierre-loup.gosse@smile.fr>
Reviewed-by: Martin Schwan <m.schwan@phytec.de>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>