Update to RGBDS 0.7.0

[Rangi42]

These new features are used from RGBDS 0.7.0:

• Use SIZEOF and STARTOF for section types, instead of *RAM_Begin/End constants
• Use ENDSECTION at the end of INCLUDEd files which start their own SECTIONs
  • These can be found via:
    for f in `git grep -Elw '^SECTION'`; do git grep -ho "INCLUDE \"$f\""; done
• DMARoutineEnd can be .End since ENDL restores scope

Also rgbdscheck.asm is rewritten to be more robust with older versions of RGBDS. (We can't define constants since DEF is required in 0.7.0 but not yet defined in old enough versions; likewise for backslash line continuations, ELIF, etc.)

Note that the object file revision is still 9, so tools/unnamed.py did not need updating.