greybus: Explicitly mark structures as packed

These structures are already marked as __packed, as these are enclosed
within:

	#pragma pack(push, 1)
	#pragma pack(pop)

Lets mark them __packed explicitly.

Reviewed-by: Alex Elder <elder@linaro.org>
Reviewed-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>