staging: et131x: Move function declarations from et131x.h to et131x.c

The function declarations in et131x.h are no longer used now all
functions are in one file. Removed declarations from et131x.h and
added any required forward declarations to et131x.c.

Signed-off-by: Mark Einon <mark.einon@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>