x86, es7000: remove externs

Impact: cleanup

In the subarch times there were a number of externs between
various bits of the ES7000 code. Now that there's a single
es7000-platform support file, the externs can be removed and
the functions can be changed the statics.

Beyond the cleanup factor, this also shrinks the size of the
kernel image a bit:

arch/x86/kernel/es7000_32.o:

   text	   data	    bss	    dec	    hex	filename
   2813	    192	     44	   3049	    be9	es7000_32.o.before
   2693	    192	     44	   2929	    b71	es7000_32.o.after

Signed-off-by: Ingo Molnar <mingo@elte.hu>