qspi: stm32: Add support for reset cmd on init

If the flash is used in 4-byte addressing, reading SFDP will fail after
a system reset if the flash isn't power cycled or hardware reset, since
Zephyr will try to use 3-byte addressing while the flash (still) expects
4-byte addressing.

This commit adds the ability to send a reset command to the flash as part
of initialization, which complements the existing reset-gpio
functionality, and is useful on low-pincount flashes which do not have a
hardware reset.

Signed-off-by: Ole Morten Haaland <omh@icsys.no>