sgi/rd: drop kvm script as buildroot suffice kvm testing

Buildroot model script is sufficient to boot the system with necessary
infrastructure to do kvm testing, such as multiple VM launch using
kvmtool. So drop the kvm script in favor of buildroot script.

Signed-off-by: Vivek Gautam <vivek.gautam@arm.com>
Change-Id: I939205f0af02f51d03e09299f439d612a70a6ff6