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>