Input: synaptics - fix handling of 2-button ClickPads

Lenovo S10-3t's ClickPad is a 2-button ClickPad that reports BTN_LEFT
and BTN_RIGHT as normal touchpad, unlike the 1-button ClickPad used in
HP mini 210 that reports solely BTN_MIDDLE.

In 0xc0-cap response, the 1-button ClickPad has the 20-bit set while
2-button ClickPad has the 8-bit set.

This patch makes the kernel only handle 1-button ClickPad specially,
and treat 2-button ClickPad in the same fashion as regular touchpads.

This fixes kernel bug #18122 and MeeGo bug #4807.

Signed-off-by: Yan Li <yan.i.li@intel.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>