flow: pass CTS_DPL_DISPLACEMENT to post-CTS detailed_placement

Seed `dpl_args` from `env_var_or_empty CTS_DPL_DISPLACEMENT` instead
of the empty list, so callers can pass extra flags (typically
`-max_displacement <row> <site>`) to the detailed_placement run
immediately after CTS without having to fork the script.

When the env var is unset, `env_var_or_empty` returns "" and the
`{*}$dpl_args` expansion is a no-op — behavior matches the prior
`{}` initialization exactly.

Signed-off-by: Øyvind Harboe <oyvind.harboe@zylin.com>

Author: oharboe

flow/scripts/cts.tcl

@@ -46,7 +46,7 @@ set_placement_padding -global \
   -left $::env(CELL_PAD_IN_SITES_DETAIL_PLACEMENT) \
   -right $::env(CELL_PAD_IN_SITES_DETAIL_PLACEMENT)
 
-set dpl_args {}
+set dpl_args [env_var_or_empty CTS_DPL_DISPLACEMENT]
 append_env_var dpl_args USE_NEGOTIATION -use_negotiation 0
 set result [catch { log_cmd detailed_placement {*}$dpl_args } msg]
 if { $result != 0 } {