Input: wacom: Add support for three new ISDv4 sensors

This patch adds support for the 0x4004, 0x5000, and 0x5002 sensors found
on what should be the Motion R12, Fujitsu Q704, and Fujitsu T904. These
tablets use a new report ID (3) for their touch packets and a slightly
different HID descriptor format, but are otherwise largely identical in
protocol to the "MTTPC" tablets.

Note:
 * The R12 uses its 0x4004 sensor for touch input only. A pen interface
   is not present in its HID descriptor, though its possible a 0x4004
   may be used for pen input by other tablet PCs in the future.

 * The 0x5002 sensor appears to use a new report ID (8) for its pen
   packets. The other sensors continue to use the traditional report
   ID (2).

Signed-off-by: Jason Gerecke <killertofu@gmail.com>
Input: wacom: Use unaligned access where necessary

A few caes of incorrectly using 'le16_to_cpup' instead of
'get_unaligned_le16' have been noticed and fixed.

Signed-off-by: Jason Gerecke <killertofu@gmail.com>