support/scripts/fix-rpath: parallelize patching files

support/scripts/fix-rpath: parallelize patching files

Using "xargs" instead of "while read" loop allows for the patching of
files to be parallelized. This significantly reduces the amount of
time it takes to fix all the paths.  On a larger RFS(~300MB) this
script was taking 5 minutes, it now only takes about 30s on a 12 core
machine.

Signed-off-by: Victor Dumas <[email protected]>
[Thomas: take into account the suggestion of Quentin Schulz to pass
PARALLEL_JOBS through the environment down to the fix-rpath script]
Signed-off-by: Thomas Petazzoni <[email protected]>