ARM: dts: renesas: genmai: Add FLASH nodes

Add device nodes for the dual Spansion S25FL512S QSPI NOR FLASH and the
two Spansion S29GL512S CFI NOR FLASHes on the Genmai development board.
The former is mapped directly through the SPI Multi I/O Bus Controller.
The latter reside in the address space of the Bus State Controller
(BSC).

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/53c89c70c6b010702fd9ab5247e19986857671ba.1693481518.git.geert+renesas@glider.be