arm64: dts: renesas: ulcb: Add RPC HyperFlash device node

Add the RPC HyperFlash device node along with its partitions to the
common ULCB board DTS file.

Based on a patch in the BSP by Valentine Barshak.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/61a63e819d4296760ca7ae83ef5226a2c4d7bd93.1648548339.git.geert+renesas@glider.be