boards: Add cs-high-time for all STM32 boards using QSPI flash

This commit set the value of the cs-high-time property for all
STM32-based boards defined in Zephyr and having a QSPI flash memory.
The value is chosen according to the flash memory requirements (often
named 'tSHSL' in the datasheets) and the maximum QSPI frequency.

Signed-off-by: Thomas Altenbach <altenbach.thomas@gmail.com>