qemu/qemu_v8: synchronize build scripts

Qemu and qemu_v8 are almost built the same way. Main differences are
32b/64b modes and u-boot/edk2 as non-secure boot stage.

optee-client targets are removed since now built from the buildroot
target.

This change also ensures on can run 'make run-only' after 'make all'
without rootfs not being copied to the output image directory.

Signed-off-by: Etienne Carriere <etienne.carriere@linaro.org>
Acked-by: Jerome Forissier <jerome.forissier@linaro.org>