HID: alps: add support for Alps T4 Touchpad device

- Define T4 device specification value for support T4 device.

- Creeate "t4_contact_data" and "t4_input_report" structure for decoding and
  storing T4-specific data

- Create "t4_calc_check_sum()" function for calculating checksum value to send
  to the device. T4 needs to send this value when reading or writing device
  address value.

- Create "t4_read_write_register()" function for reading and writing device
  address value.

- Create "t4_raw_event()" function for decodin XYZ, palm and button data.

- Replace "MAX_TOUCHES" fixed variable to "max_fingers" variable.

- Add T4 devuce product ID. (0x120C)

T4 device is used on HP EliteBook 1000 series and Zbook Stduio

[jkosina@suse.cz: rewrite changelog]
Signed-off-by: Masaki Ota <masaki.ota@jp.alps.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>