loveplus: stub impl of cpusbxpkm.dll (printer) (#319)

## Link to GitHub Issue, if one exists
n/a

## Description of change
Add a stub for `cpusbxpkm.dll`. The stub doesn't work, it's only enough
to allow the game to load; but that is irrelevant since spice hooks the
printer at runtime.

## Testing
Observed the game boot, and was able to print out the test image from
test menu. Will do more testing on a real server.

src/spice2x/stubs/cpusbxpkm.def

@@ -0,0 +1,18 @@
+EXPORTS
+    CPU9CheckPaperRemain
+    CPU9CheckPrinter
+    CPU9CheckPrintEnd
+    CPU9GetFWInfo
+    CPU9GetMediaType
+    CPU9GetTempInfo
+    CPU9GetTotalPrintCount
+    CPU9PreHeat
+    CPU9PrintJobCancel
+    CPU9PrintOut
+    CPU9SetPrintParameter2
+    CPUASendImage
+    CPUASendImagePrint
+    CPUASendImagePrint2
+    CPUASetPrintParameter
+    CPUXInit
+    CPUXSearchPrinters