sparc64: Rework auxio driver to save some text space.

Use common functions instead of inlining and duplicating logic
over and over to handle the SBUS vs. EBUS cases.

Before:

   text	   data	    bss	    dec	    hex	filename
    715	    568	     16	   1299	    513	arch/sparc64/kernel/auxio.o

After:

   text	   data	    bss	    dec	    hex	filename
    631	    568	     16	   1215	    4bf	arch/sparc64/kernel/auxio.o

Signed-off-by: David S. Miller <davem@davemloft.net>