ARM: dts: renesas: rskrza1: Add FLASH nodes

Add device nodes for the dual Spansion S25FL512S QSPI NOR FLASH and the
Spansion S29GL512S CFI NOR FLASH on the RSK+RZA1 development board.
The former is mapped directly through the SPI Multi I/O Bus Controller.
The latter resides in the external address space of the Bus State
Controller (BSC).

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/17a221699da14639e72264ffa39d47592d470f9a.1693481518.git.geert+renesas@glider.be