[SPARC64]: Add -mtune=ultrasparc3 if possible.

This gives better heuristics for the cost of a multiply (fixed
5 cycles), rather than the 'ultrasparc' setting (variable, and
unpredictable if the second argument is non-constant).

Example code size savings:

   text	   data	    bss	    dec	    hex	filename
3823690	 304040	 448880	4576610	 45d562	vmlinux
3824521	 304040	 448880	4577441	 45d8a1	vmlinux.orig
Signed-off-by: David S. Miller <davem@davemloft.net>

arch/sparc64/Makefile

@@ -17,6 +17,7 @@ LDFLAGS		:= -m elf64_sparc
 KBUILD_CFLAGS += -m64 -pipe -mno-fpu -mcpu=ultrasparc -mcmodel=medlow \
 	-ffixed-g4 -ffixed-g5 -fcall-used-g7 -Wno-sign-compare \
 	-Wa,--undeclared-regs
+KBUILD_CFLAGS += $(call cc-option,-mtune=ultrasparc3)
 KBUILD_AFLAGS += -m64 -mcpu=ultrasparc -Wa,--undeclared-regs
 
 ifeq ($(CONFIG_MCOUNT),y)