u-boot: use array instead of sting concatenation

This will make it easier to work on #256

Signed-off-by: Rémi Duraffort <remi.duraffort@linaro.org>
15 jobs for uboot in 10 minutes and 6 seconds (queued for 4 seconds)
latest
Status Job ID Name Coverage
  Test
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amd64
dispatcher-debian-10

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passed #57235
amd64
dispatcher-debian-9

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amd64
server-debian-10

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passed #57236
amd64
server-debian-9

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  Analyze
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amd64
black

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code_quality

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dockerfiles

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job-schema

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pylint

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amd64-dind allowed to fail
sast

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  Build
passed #57247
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amd64/pkg-debian-10

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passed #57246
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amd64/pkg-debian-9

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passed #57245
amd64
doc

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  Docker
passed #57248
amd64-dind
amd64/lava-dispatcher

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passed #57249
amd64-dind
amd64/lava-server

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