board: rockchip: Add Radxa ROCK 5 ITX

board: rockchip: Add Radxa ROCK 5 ITX

The Rock 5 ITX is a board in ITX form factor using the RK3588 SoC

It can be powered either by 12V, ATX power-supply or PoE.

Notable peripherals are the 4 SATA ports, M.2 M-Key slot, M.2 E-key slot,
2*2.5Gb PCIe-connected Ethernet NICs.

Display options are 2*HDMI, DP via USB-c, eDP + 2*DSI via PCB connectors.

USB ports are 4*USB3 + 2*USB2 on the back panel and 2-port front-panel
connector.

Schematics for the board can be found on
- https://dl.radxa.com/rock5/5itx/radxa_rock_5_itx_X1100_schematic.pdf
- https://dl.radxa.com/rock5/5itx/v1110/radxa_rock_5itx_v1110_schematic.pdf

The naming scheme with the dashes follows Dragan's comment on the mainline
devicetree commit:
    "the name of this board deviates from the standard Radxa naming scheme,
     which is something like "ROCK <number><letter>" thus, "rock-5a" is
     fine, but it should be "rock-5-itx", simply because there's a space
     between "5" and "ITX" in "ROCK 5 ITX"

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
Signed-off-by: Kever Yang <kever.yang@rock-chips.com>