CBMEM: Tidy up CAR migration

Move the  CAR migration call to arch -specific part of CBMEM init,
it is truly a x86 specific thing.

Change-Id: I715417e54f197b8745e0670d6b900a5660178141
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/7860
Reviewed-by: Aaron Durbin <adurbin@google.com>
Tested-by: build bot (Jenkins)

src/arch/arm/include/arch/early_variables.h

@@ -27,6 +27,5 @@ static inline void *car_get_var_ptr(void *var) { return var; }
 #define car_get_var(var) (var)
 #define car_sync_var(var) (var)
 #define car_set_var(var, val) do { (var) = (val); } while (0)
-static inline void car_migrate_variables(void) { }
 
 #endif