Move the byte-order-swapping helpers from ptp-pack.c to ptp.h as well as 2
ptp_free_deviceinfo variants and remove all but one ptp-pack.c inclusions.

This speeds up compile time and removes lots of compiler warning
repetitions if one shows up in ptp-pack.c.

Layout this one case block just like the other ones. This is basically a
whitespace only change.

PTPDeviceProperty data of EOS cameras is not polled but rather pro-actively
sent by the camera via a PropValueChanged event. The unpack function used
to interpret the data and unpack it into the PTPDevicePropDesc struct
but also copied the raw event data block into an extra member (data, size)
of the special special PTPCanon_Property struct. This data is then never
looked at again.

This patch removes those data members and is a first step to completely
eliminate the special PTPCanon_Property struct.

Make the names more consistent and expressive.

The proptype (a.k.a. device property code) is already stored in
dpd.DevicePropertyCode member. This patch introduces the
ptp_find_eos_devicepropdesc() function for the commonly repeated for-loop
looking for the DevicePropDesc* in the cache.

This now allows to completely replace PTPCanon_Property with
PTPDevicePropDesc and then drop the canon_props array altogether and use
the generic one.

The current value of the device property is only stored in the
desc.CurrentValue field.

…ack.c"