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.

install/romm.json

@@ -3605,6 +3605,7 @@
         "sega-mega-cd"
       ],
       "regions": [
+        "latin-america",
         "north-america"
       ],
       "region_system_groups": [
@@ -5667,12 +5668,6 @@
       ],
       "systems": [
         "sony-playstation"
-      ],
-      "regions": [
-        "japan"
-      ],
-      "region_groups": [
-        "sony-playstation"
       ]
     },
     {
@@ -12866,7 +12861,8 @@
         "nintendo-gamecube"
       ],
       "regions": [
-        "japan"
+        "japan",
+        "south-korea"
       ],
       "region_groups": [
         "Dolphin:file:ngc/dolphin-emu/Sys/GC/JAP/IPL.bin"
@@ -13558,6 +13554,7 @@
         "sega-mega-cd"
       ],
       "regions": [
+        "latin-america",
         "north-america"
       ],
       "region_groups": [
@@ -13578,6 +13575,7 @@
         "sega-mega-cd"
       ],
       "regions": [
+        "latin-america",
         "north-america"
       ],
       "region_groups": [
@@ -13598,6 +13596,7 @@
         "sega-mega-cd"
       ],
       "regions": [
+        "latin-america",
         "north-america"
       ],
       "region_groups": [
@@ -13823,7 +13822,8 @@
         "nintendo-gamecube"
       ],
       "regions": [
-        "japan"
+        "japan",
+        "south-korea"
       ],
       "region_groups": [
         "PrimeHack:file:ngc/GC/JAP/IPL.bin"