Start moving pokenav data into C files

The types and usage of many of the globals are now known.

ld_script.txt

@@ -592,6 +592,7 @@ SECTIONS {
         src/pokemon_summary_screen.o(.rodata);
         src/unk_pokedex_area_screen_helper.o(.rodata);
         src/battle_pyramid_bag.o(.rodata);
+        src/pokenav_main.o(.rodata);
         data/pokenav.o(.rodata);
         src/pokenav_match_call.o(.rodata);
         data/rom_81D1C44.o(.rodata);