OpenLane support for other sky130 variants

- Added support for ls, ms, hdll, and hvl
- power nets are named after the VDD and GND pin names; makes LVS report super
  clean
- Added support for both EF_STYLEs in OpenLane configuration files
diff --git a/sky130/openlane/common_pdn.tcl b/sky130/openlane/common_pdn.tcl
index 60ad840..872688a 100644
--- a/sky130/openlane/common_pdn.tcl
+++ b/sky130/openlane/common_pdn.tcl
@@ -1,6 +1,6 @@
 # Power nets
-set ::power_nets "VDD"
-set ::ground_nets "VSS"
+set ::power_nets $::env(VDD_PIN)
+set ::ground_nets $::env(GND_PIN)
 
 set ::macro_blockage_layer_list "li1 met1 met2 met3 met4 met5"