Add board file for the RK3588 Rock 5B board. This is a basic
implementation which just brings up the eMMC and UART which is
enough to successfully boot Linux.

The ethernet controller is connected via PCIe so support will
come in a follow-up patch.
Signed-off-by: Christopher Obbard <chris.obbard@collabora.com>
Reviewed-by: Michael Riesch <michael.riesch@wolfvision.net>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Link: https://lore.kernel.org/r/20230109155801.51642-8-sebastian.reichel@collabora.comSigned-off-by: Heiko Stuebner <heiko@sntech.de>