get rid of duplicate logics in __SC_....[1-6] definitions

All those guys have the same form - "take a list of type/name pairs,
apply some macro to each of them".  Abstract that part away, convert
all __SC_FOO##x(__VA_ARGS__) to __MAP(x,__SC_FOO,__VA_ARGS__).

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>