HID: elecom: refer to trackballs by model name instead of series

This patch changes all references to ELECOM trackballs using their
series name to refer to them by their model name.

ELECOM provides multiple series of mice such as EX-G, HUGE, and DEFT.
Although it has not caused conflicts in the driver, there can be more
than one iteration of mice in each series. For example, there are 7
variants of EX-G trackballs but only three (M-XT3URBK, M-XT3DRBK, and
M-XT4DRBK) need a driver to work correctly.

There are also 4 DEFT series trackballs but two of them have the same
VID:PID as the other two. I picked the earlier model for the naming of
the PID macros.

Signed-off-by: Tomasz Kramkowski <tk@the-tk.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>