Linux: Move headless config sed file

Signed-off-by: Anton Kolesov <Anton.Kolesov@synopsys.com>
Linux: Do not remove namespaces support in headless builds

Do not remove support for Linux namespaces in headless script. Add comment that
describes what this script does.

Signed-off-by: Anton Kolesov <Anton.Kolesov@synopsys.com>
Linux: Handle defconfing sed files better

Sed script files must have extension .sed.

Signed-off-by: Anton Kolesov <Anton.Kolesov@synopsys.com>
fixup! Linux: Do not remove namespaces support in headless builds
Linux: Add more defconfig sed scripts

Signed-off-by: Anton Kolesov <Anton.Kolesov@synopsys.com>