fix: tag regions by the branch the code takes

Mega CD US BIOS serves every non-EU, non-JP disc; Dolphin boots
Korean discs from the JAP directory; Beetle never opens scph5903.bin
under that name.

emulators/primehack.yml

@@ -52,7 +52,7 @@ files:
 
   - name: "IPL.bin"
     path: "GC/JAP/IPL.bin"
-    region: [japan]
+    region: [japan, south-korea]
     size: 2097152
     required: false
     hle_fallback: true