86xx: Remove redudant PLATFORM_CPPFLAGS

For historic reasons we had defined some additional PLATFORM_CPPFLAGS like:

PLATFORM_CPPFLAGS += -DCONFIG_MPC86xx=1
PLATFORM_CPPFLAGS += -DCONFIG_MPC8641=1

However these are all captured in the config.h and thus redudant.  Also
moved common 86xx flags into cpu/mpc86xx/config.mk.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
diff --git a/cpu/mpc86xx/config.mk b/cpu/mpc86xx/config.mk
index d767269..13da2cf 100644
--- a/cpu/mpc86xx/config.mk
+++ b/cpu/mpc86xx/config.mk
@@ -23,4 +23,5 @@
 
 PLATFORM_RELFLAGS += -fPIC -ffixed-r14 -meabi
 
-PLATFORM_CPPFLAGS += -DCONFIG_MPC86xx -ffixed-r2 -mstring
+PLATFORM_CPPFLAGS += -ffixed-r2 -mstring
+PLATFORM_CPPFLAGS += -maltivec -mabi=altivec -msoft-float