This commit adds support for SPI NOR flash on Radxa ROCK 5B.

SPI NOR flash chip may vary, so use safe(lowest) spi-max-frequency.
Signed-off-by: FUKAUMI Naoki <naoki@radxa.com>
Link: https://lore.kernel.org/r/20240623023329.1044-1-naoki@radxa.comSigned-off-by: Heiko Stuebner <heiko@sntech.de>