Input: synaptics - fix device info appearing different on reconnect

User-modified input settings no longer survive a suspend/resume cycle.
Starting with 4.12, the touchpad is reinitialized on every reconnect
because the hardware appears to be different. This can be reproduced
by running the following as root:

    echo -n reconnect >/sys/devices/platform/i8042/serio1/drvctl

A line like the following will show up in dmesg:

    [30378.295794] psmouse serio1: synaptics: hardware appears to be
                   different: id(149271-149271), model(114865-114865),
                   caps(d047b3-d047b1), ext(b40000-b40000).

Note the single bit difference in caps: bit 1 (SYN_CAP_MULTIFINGER).

This happens because we modify our stored copy of the device info
capabilities when we enable advanced gesture mode but this change is
not reflected in the actual hardware capabilities.

It worked in the past because synaptics_query_hardware used to modify
the stored synaptics_device_info struct instead of filling in a new
one, as it does now.

Fix it by no longer faking the SYN_CAP_MULTIFINGER bit when setting
advanced gesture mode. This necessitated a small refactoring.

Fixes: 6c53694f ("Input: synaptics - split device info into a separate structure")
Signed-off-by: Anthony Martin <ality@pbrane.org>
Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>