cpu/x86/mp: use __aligned macro

Now that __aligned is around, take advantage of it.

Change-Id: I93cdbe108d752088f34d3f5722dce5d9b90bcdc3
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/26022
Reviewed-by: Justin TerAvest <teravest@chromium.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/cpu/x86/mp_init.c

@@ -60,7 +60,7 @@ struct mp_flight_record {
 	atomic_t cpus_entered;
 	mp_callback_t ap_call;
 	mp_callback_t bsp_call;
-} __attribute__((aligned(CACHELINE_SIZE)));
+} __aligned(CACHELINE_SIZE);
 
 #define _MP_FLIGHT_RECORD(barrier_, ap_func_, bsp_func_) \
 	{							\