Move common parts shared with GS1920-24HPv2 from v1's DTS and image
definition into a common DTSI and device definition to prepare adding
support for GS1920-24HPv2.
Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/21944
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>