ARM7TDMI: remove forward decls

The forward decls are just code clutter; remove them, by moving
their references after definitions.  This is another file which
never needed even one internal forward declaration.

Also shrink a few overly-long lines with function declarations
or definitions;  get rid of arm7tdmi_register_commands(), it's
not needed (just delegated); minor whitespace declutter.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>