For other parties using the stats interface with the softpll we need
the minimal file that can be easily used in other projects (like SNMP on
the wr-switch).

Move to the softpll_export.h:
--struct spll_stats
--defines of seq_state from softpll_ng.c (SEQ_* and AUX_*)
--defines of align_state from spll_external.c (ALIGN_*)
--defines of mode from softpll_ng.h (SPLL_MODE_*)
Signed-off-by: Adam Wujek <adam.wujek@cern.ch>