Revert "HID: i2c-hid: Disable runtime PM on Synaptics touchpad"

This reverts commit 74e7c6c8.

It finally turns out the touchpad is an engineering sample and it is
not the Synaptics touchpad. Let us revert this patch otherwise it will
affect the real Synaptics touchpad.

Signed-off-by: Hui Wang <hui.wang@canonical.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>