cmake: product/juno

This change adds CMake build system support for product/juno

Please note that firmware targets do not use libRTX_CM3.a
or RTX_CM3.lib, instead in CMake build, the library
is built using sources.

Change-Id: Iefcad29d75fc240237295295f224278254cdc9fd
Signed-off-by: Girish Pathak <girish.pathak@arm.com>