HID: wacom: retrieve name from HID descriptor for generic devices

HID generic devices share the same default name, "Wacom HID". This
causes userland programs to show same device names for different
devices, which would confuse end users with same device names for
different devices too.

This patch uses name retrieved from HID descriptor, if a meaningful
name is reported. Otherwise, affix its product ID to "Wacom HID".

Names from descriptor may contain extra whitespaces. To comfort
readers' eyes, we removed those extra whitespaces too.

Signed-off-by: Ping Cheng <pingc@wacom.com>
Reviewed-by: Jason Gerecke <killertofu@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>