mpc85xx: Add support for -msingle-pic-base

mpc85xx: Add support for -msingle-pic-base

-msingle-pic-base is a new gcc(from 4.6) option for ppc and
it reduces the size of my u-boot with about 4-5 KB.
While at it, add -fno-jump-tables too to save a
few more bytes.

e5500 core:
size u-boot.bef
   text	   data	    bss	    dec	    hex	filename
 473043	  23772	 307104	 803919	  c444f	u-boot.bef
size u-boot.aft
   text	   data	    bss	    dec	    hex	filename
 453195	  23772	 307104	 784071	  bf6c7	u-boot.aft

e500 core:
size u-boot.bef
   text	   data	    bss	    dec	    hex	filename
 292998	  17868	  24968	 335834	  51fda	u-boot.bef
size u-boot.aft
   text	   data	    bss	    dec	    hex	filename
 288002	  17868	  24968	 330838	  50c56	u-boot.aft

Signed-off-by: Joakim Tjernlund <joakim.tjernlund@infinera.com>
Reviewed-by: York Sun <york.sun@nxp.com>