devicetree: i2c-hid: Add regulator support

Document a "vdd-supply" and an initialization delay. Can be used for
powering on/off a HID.

Signed-off-by: Caesar Wang <wxt@rock-chips.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: linux-input@vger.kernel.org
Signed-off-by: Brian Norris <briannorris@chromium.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>