Rename __attribute__((packed)) --> __packed

Also unify __attribute__ ((..)) to __attribute__((..)) and
handle ((__packed__)) like ((packed))

Change-Id: Ie60a51c3fa92b5009724a5b7c2932e361bf3490c
Signed-off-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-on: https://review.coreboot.org/15921
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

payloads/libpayload/include/arm64/arch/exception.h

@@ -39,7 +39,7 @@ struct exception_state
 	uint64_t elr;
 	uint64_t esr;
 	uint64_t regs[31];
-} __attribute__((packed));
+} __packed;
 
 extern struct exception_state *exception_state;