85xx: Use gc-sections to reduce image size

On an XPedite5370 over 11KBytes were saved:
  Before:
       text	   data	    bss	    dec	    hex	filename
   332456	  33364	  33476	 399296	  617c0	./u-boot

  After:
      text	   data	    bss	    dec	    hex	filename
   321075	  33836	  33476	 388387	  5ed23	./u-boot

Signed-off-by: Peter Tyser <ptyser@xes-inc.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>