boards: qemu_x86: Do not build "raw" binary for qemu

Do not build "raw" binary for qemu boards. It was already disabled for
all qemu boards except for qemu_x86_64. This also prevents exposing
bug with llvm when building "raw" binary using unsupported options in
objcopy.

Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@intel.com>