Add zynq-miami-7030 and zynq-miami-7015 machines

"zynq-miami" is now a SOC_FAMILY, so its overrides are still valid. And
since the regex "zynq-miami" also matches "zynq-miami-7030", the
COMPATIBLE_MACHINE directives will also still work. However, you must
set the MACHINE environment to either zynq-miami-7030 or zynq-miami-7015
now.

They are basically the same boards, only a different Zynq chip.