HID: intel-ish-hid: Hide members of struct ishtp_cl_device

ISH clients don't need to access any field of struct ishtp_cl_device. To
avoid this create an interface functions instead where it is required.
In the case of ishtp_cl_allocate(), modify the parameters so that the
clients don't have to dereference.
Clients can also use tracing, here a new interface is added to get the
common trace function pointer, instead of direct call.
The new interface functions defined in one external header file, named
intel-ish-client-if.h. This is the only header files all ISHTP clients
must include.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>