libfdt-dev is needed when building kernels for architectures that
support a device tree.
Fixes build errors like these when building kvm+lkvm flavor for
ARM64:
Makefile: No libfdt found. Please install libfdt-dev package. Stop.
Signed-off-by: Geoff Levand <geoff@infradead.org>
We depend on libacl development headers but we forgot to update the
scripts to build rkt in rkt.
Also, update the one-liners mentioned in the documentation.