HID: wacom: Split apart 'wacom_setup_pentouch_input_capabilites'

This splits the 'wacom_setup_pentouch_input_capabilites' function into
pieces dedicated to doing setup for just the pen interface and just
the touch interface. This makes it easier to focus on the relevant
piece when making changes.

This patch introduces no functional changes.

Signed-off-by: Jason Gerecke <jason.gerecke@wacom.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>