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: NKumar Gala <galak@kernel.crashing.org>

cpu/mpc85xx/config.mk

@@ -25,3 +25,4 @@ PLATFORM_RELFLAGS += -fPIC -ffixed-r14 -meabi
 
 PLATFORM_CPPFLAGS += -DCONFIG_MPC85xx -DCONFIG_E500 -ffixed-r2 \
 			-Wa,-me500 -msoft-float -mno-string
+PLATFORM_CPPFLAGS +=$(call cc-option,-mno-spe)