No functional changes: Introduces a barebox-package function towards
re-use by a 2nd config build.
Because the function is meant to be called from within a $(eval), all
instances of '$' has to be escaped. I.e. rename '$' -> '$$'.
Signed-off-by: Pieter Smith <pieter@boesman.nl>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>