Add FuseSoC support for spm design

This adds a core description file for the spm core that exposes targets
for linting and for building a GDSII using OpenLANE.

Quick FuseSoC instructions:

 #install FuseSoC
pip3 install fusesoc
 #Create and enter a new workspace
mkdir workspace && cd workspace
 #Register spm as a library in the workspace
fusesoc library add spm /path/to/spm
 #...if repo is available locally or...
fusesoc library add spm https://github.com/The-OpenROAD-Project/OpenLane
 #...to get the upstream repo

 #To run lint
fusesoc run --target=lint efabless::spm
 #To build with OpenLANE running in a docker container
EDALIZE_LAUNCHER=el_docker fusesoc run --target=sky130 efabless::spm
 #List all targets
fusesoc core show efabless::spm

designs/spm/sky130.tcl

@@ -0,0 +1,9 @@
+set ::env(DESIGN_NAME) "spm"
+set ::env(CLOCK_PERIOD) 10
+set ::env(CLOCK_PORT) "clk"
+set ::env(CLOCK_NET) "clk"
+set ::env(FP_PDN_VOFFSET) 7
+set ::env(FP_PDN_HOFFSET) 7
+set ::env(FP_PIN_ORDER_CFG) "pin_order.cfg"
+set ::env(FP_PDN_SKIPTRIM) true
+set ::env(FP_CORE_UTIL) 45

designs/spm/spm.core

@@ -0,0 +1,28 @@
+CAPI=2:
+
+name : efabless::spm:0
+
+filesets:
+  rtl:
+    files: [src/spm.v : {file_type : verilogSource}]
+
+  sky130:
+    files:
+      - pin_order.cfg : {file_type : user, copyto : .}
+      - sky130.tcl : {file_type : tclSource}
+
+targets:
+  default:
+    filesets : [spm]
+
+  lint:
+    default_tool : verilator
+    filesets : [rtl]
+    tools:
+      verilator: {mode: lint-only}
+    toplevel: spm
+
+  sky130:
+    default_tool : openlane
+    filesets: [rtl, sky130]
+    toplevel : spm