Reverted the __packed and __aligned change.

We should not add compiler extensions, it is not our job. We are not a
selfcontained project as kernel is so we should not introduce things
like this.

If we need to add some abstraction for this in the future to support
compilers doing these things differently then we will do that the same
way we dealt with the depricated attribute.

include/libopencm3/usb/dfu.h

@@ -94,7 +94,7 @@ struct usb_dfu_descriptor {
 	uint16_t wDetachTimeout;
 	uint16_t wTransferSize;
 	uint16_t bcdDFUVersion;
-} __packed;
+} __attribute__((packed));
 
 #endif