genksyms: Simplify printing of symbol types

Instead of special-casing SYM_NORMAL, do not map any name to it. Also
explicitly set the single-letter name of the symbol type, which will be
needed by a further patch. The only user-visible change is one debug
printf.

Signed-off-by: Michal Marek <mmarek@suse.cz>
Acked-by: Sam Ravnborg <sam@ravnborg.org>