Input: wacom - report resolution for pen devices

Touch resolution is reported to the userland by retrieving the value
from the HID descriptor. But pen resolution is not since it can not
be retrieved. The current Wacom X driver has a resolution table.
To centralize the source of these values, the resolution entries are
added in the wacom_features struct for x and y coordinates respectively.
The values are then reported to the userland.

Signed-off-by: Ping Cheng <pingc@wacom.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>