mediatek: EX5601-T0 add Zyxel EX5601-T1 and T-56 alias

mediatek: EX5601-T0 add Zyxel EX5601-T1 and T-56 alias

Define EX5601-T1 and T-56 as alternative name, to explicitly show
the device is supported using existing image. EX5601-T1 does not
have the option to switch between WAN/SFP port. The switch port
is hardwired to the WAN port. The Zyxel T-56 is the odido-branded
version of the EX5601-T1.

Signed-off-by: Aleksander Jan Bajkowski <olek2@wp.pl>
Link: https://github.com/openwrt/openwrt/pull/17615
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
(cherry picked from commit 3d63a41ffab69cb6f49c14cff99c3c3a84899363)