Integrate config/kirkstone-add-multiconfig-handling

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Commit: config@96799c56



setup-environment: automate adding of available multiconfigs to local.conf

If MULTICONFIG=true parameter is passed to setup-environment script, it
will enable multiconfig in local.conf if multiconfigs configurations were
found in layers.

Signed-off-by: Mikhail Vanyulin <mikhail.vanyulin@rtsoft.de>