Input: cap11xx - add support for cap1206

According to the datasheet "The CAP1206 is pin- and register-compatible
with the CAP1106, with the exception of the GAIN[1:0] bits and ALT_POL
bit"(57). So, this patch aims to disable them as they are no longer
used.

Signed-off-by: Jesse Taube <mr.bossman075@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>