scripts/dts: Change DT_<COMPAT>_<INSTANCE>_<PROP> define

Its possible that the <INSTANCE> number could conflict with the register
number.  This is shown to happen for a device like soc-nv-flash at
address 0.

So change naming convention to DT_INST_<INSTANCE>_<COMPAT>_<PROP> and
make DT_<COMPAT>_<INSTANCE>_<PROP> as deprecated.

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>