HID: wacom: consolidate input capability settings for pen and touch

After PAD moved to its own interface, there were duplicated statements in
wacom_setup_pentouch_input_capabilities. Merge them together to reduce future
maintenance effort.

Signed-off-by: Ping Cheng <pingc@wacom.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>