This commit has no effect on the final binary file.

The state structures for softpll_ng must be accessed by tools/wrpc-dump,
so we need them in an header (not in sofpll_mg.c itself).

Unfortunately, struct softpll_state includes a lot of other structures,
so all dependent headers must be included by softpll_ng.h.  Thus,
all C files should now include softpll_ng.h alone, not the other ones.

I also had to remove inclusion of unneeded <stdint.h> and <stdlib.h>
from spll_common.h, because stdlib pulled the prototype for abs()
which is #defined in ppsi (my bad!), and we would have a build error.
Signed-off-by: Alessandro Rubini <rubini@gnudd.com>