board: rockchip: Add FriendlyElec CM3588 NAS

The CM3588 NAS by FriendlyElec pairs the CM3588 compute module, based
on the Rockchip RK3588 SoC, with the CM3588 NAS Kit carrier board.

Features tested on a CM3588 NAS Kit with 8GB RAM 64GB eMMC module:
- SD-card boot
- eMMC boot
- Ethernet
- PCIe/NVMe
- USB gadget
- USB host

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/doc/board/rockchip/rockchip.rst b/doc/board/rockchip/rockchip.rst
index 7003f05..7523c01 100644
--- a/doc/board/rockchip/rockchip.rst
+++ b/doc/board/rockchip/rockchip.rst
@@ -127,6 +127,7 @@
      - Rockchip EVB (evb-rk3588)
      - Edgeble Neural Compute Module 6A SoM - Neu6a (neu6a-io-rk3588)
      - Edgeble Neural Compute Module 6B SoM - Neu6b (neu6b-io-rk3588)
+     - FriendlyElec CM3588 NAS (cm3588-nas-rk3588)
      - FriendlyElec NanoPC-T6 (nanopc-t6-rk3588)
      - FriendlyElec NanoPi R6C (nanopi-r6c-rk3588s)
      - FriendlyElec NanoPi R6S (nanopi-r6s-rk3588s)