build: fix rpi3 and hikey960 builds

Replace hello-world target with new optee-examples
Replace u-boot-jtag-bin target with u-boot-rpi-bin

Acked-by: Victor Chong <victor.chong@linaro.org>
Reviewed-by: Joakim Bech <joakim.bech@linaro.org>
Signed-off-by: Igor Opaniuk <igor.opaniuk@linaro.org>