HID: Delay opening HID device

Don't call hid_open_device till there is actually an user. This saves
power by not opening underlying transport for HID. Also close device
if there are no active mfd client using HID sensor hub.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>