Add fastmem arena setting

Just for debugging.

Source/Android/app/src/main/res/values/strings.xml

@@ -399,6 +399,7 @@
     <string name="debug_submenu">Debug</string>
     <string name="debug_warning">Warning: Debug settings will slow emulation</string>
     <string name="debug_fastmem">Disable Fastmem</string>
+    <string name="debug_fastmem_arena">Disable Fastmem Arena</string>
     <string name="debug_jit_header">Jit</string>
     <string name="debug_jitoff">Jit Disabled</string>
     <string name="debug_jitloadstoreoff">Jit Load Store Disabled</string>