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/arch/arm/gdb.c

@@ -22,10 +22,10 @@ struct gdb_regs
 	struct fp_reg
 	{
 		u8 byte[12];
-	} __attribute__((packed)) f[8];
+	} __packed f[8];
 	u32 fps;
 	u32 cpsr;
-} __attribute__((packed));
+} __packed;
 
 static const u8 type_to_signal[] = {
 	[EXC_UNDEF]  = GDB_SIGILL,