freeswitch-stable: Clean up the Makefile

freeswitch-stable: Clean up the Makefile

- Fix alphabetical sorting.
- Move some of the blocks around, e.g. move everything together that
  adds to $(CONFIGURE_ARGS), move Download define upward to the other
  defines etc.
- Replace some strings with variables, e.g. $(FIND) and $(FPIC).
- Be consistent and prefix our own variables with "FS_STABLE_".
- Remove the dev package and use Build/InstallDev instead.
- All in all this change is purely cosmetic.

Signed-off-by: Sebastian Kemper <sebastian_ml@gmx.net>