Integrate buildroot into devlib in order to ease building kernel and
root filesystem images via 'generate-kernel-initrd.sh' helper script.
As its name suggests, the script builds kernel image which also includes
an initial RAM disk per default config files located under
configs/<arch>/.
Provide config files for buildroot and Linux kernel as well as a
post-build.sh script which tweaks (e.g., allowing root login on SSH)
target's root filesystem.
doc/tools.rst talks about details of kernel and rootfs configuration.
Signed-off-by: Metin Kaya <metin.kaya@arm.com>
