Input: wacom_i2c - implement hovering capability

Although BTN_TOOL_PEN and BTN_TOOL_RUBBER functioned properly, the driver
didn't have hover functionality, so it's been added.

Also, "WACOM_RETRY_CNT" was not used, so it was removed.

Signed-off-by: Tatsunosuke Tobita <tobita.tatsunosuke@wacom.co.jp>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>