Use labels instead of constants for HRAM

Use explicit ldh instruction to access HRAM locations, don't rely on optimizing ld

tools/sort_symfile.sh

@@ -7,6 +7,7 @@ sed \
     -e "s/^..:[A-B]/3_SRAM@&/g" \
     -e "s/^00:[C-D]/4_WRAM0@&/g" \
     -e "s/^..:[D-D]/5_WRAMX@&/g" \
+    -e "s/^..:[F-F]/6_HRAM@&/g" \
     $1 \
 | sort \
 | sed -e "s/^.*@//g" > $TEMP_FILE