rework the splfoo implementation so it can provide splraise.

rework the splfoo implementation so it can provide splraise.

sparc was like sparc64 (or more likely sparc64 was like sparc) in
that the spl api was build with macros that created inline functions
that the spl were implemented as. this rework provides an splraise
that the splfoo macros are defined to.

because the code sequences for spl0, splraise, and splx are relatively
long, ive turned them into functions.

tested by (and thanks go to) miod@ tobiasu@