RTH's final complaint (so far 8) was that we should sort the module
sections: archs might require some sections to be adjacent, so they can
all be reached by a relative pointer (ie.  GOT pointer).  This
implements that reordering, and simplfies the module interface for
architectures as well.

Previously an arch could specify it wanted extra space, but not where
that space would be.  The new method (used only by PPC so far) is to
allocate an empty section (in asm/module.h or by setting LDFLAGS_MODULE
to use an arch specific linker script), and expand that to the desired
size in "module_frob_arch_sections()".