change PLEPAPER_MOD_INIT macro so it can be used by modules

Re-define PLEPAPER_MOD_INIT so it can be used by loadable
modules to define their entry point symbol.  No mudules
were using the previons PLEPAPER_MOD_INIT.  It can now be
used as follows:

PLEPAPER_MOD_INIT(epdc, dev)
ChangeLog v1.6.1 -> v1.7