85xx: Add -mno-spe to e500/85xx builds

Newer gcc's might be configured to enable autovectorization by default.
If we happen to build with one of those compilers we will get SPE
instructions in random code.

-mno-spe disables the compiler for automatically generating SPE
instructions without our knowledge.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
diff --git a/cpu/mpc85xx/config.mk b/cpu/mpc85xx/config.mk
index f6df702..9e574a2 100644
--- a/cpu/mpc85xx/config.mk
+++ b/cpu/mpc85xx/config.mk
@@ -25,3 +25,4 @@
 
 PLATFORM_CPPFLAGS += -DCONFIG_MPC85xx -DCONFIG_E500 -ffixed-r2 \
 			-Wa,-me500 -msoft-float -mno-string
+PLATFORM_CPPFLAGS +=$(call cc-option,-mno-spe)