board: rockchip: add Radxa ROCK5A Rk3588 board

ROCK 5A is a Rockchip RK3588S based SBC (Single Board Computer) by Radxa.

There are tree variants depending on the DRAM size : 4G, 8G and 16G.

Specifications:

Rockchip Rk3588S SoC
4x ARM Cortex-A76, 4x ARM Cortex-A55
4/8/16GB memory LPDDR4x
Mali G610MC4 GPU
MIPI CSI 2 multiple lanes connector
4-lane MIPI DSI connector
Audio – 3.5mm earphone jack
eMMC module connector
uSD slot (up to 128GB)
2x USB 2.0, 2x USB 3.0
2x micro HDMI 2.1 ports, one up to 8Kp60, the other up to 4Kp60
Gigabit Ethernet RJ45 with optional PoE support
40-pin IO header including UART, SPI, I2C and 5V DC power in
USB PD over USB Type-C
Size: 85mm x 56mm (Raspberry Pi 4 form factor)

Kernel commits:
d1824cf95799 ("arm64: dts: rockchip: Add rock-5a board")
991f136c9f8d ("arm64: dts: rockchip: Update sdhci alias for rock-5a")
304c8a759953 ("arm64: dts: rockchip: Remove empty line from rock-5a")
cda0c2ea65a0 ("arm64: dts: rockchip: Fix RX delay for ethernet phy on rk3588s-rock5a")

Signed-off-by: Eugen Hristev <eugen.hristev@collabora.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>