powerpc: Remove unncessary SPE related compiler flag

After testing of various compiler flag combinations by Nate Case it was
determined that -mabi=no-spe has no impact on the compiler generating
SPE instructions.  Only -mno-spe and -mspe=no do.
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>

arch/powerpc/Makefile

@@ -107,7 +107,6 @@ KBUILD_CFLAGS += $(call cc-option,-mno-altivec)
 # (We use all available options to help semi-broken compilers)
 KBUILD_CFLAGS += $(call cc-option,-mno-spe)
 KBUILD_CFLAGS += $(call cc-option,-mspe=no)
-KBUILD_CFLAGS += $(call cc-option,-mabi=no-spe)
 
 # Enable unit-at-a-time mode when possible. It shrinks the
 # kernel considerably.