drivers: flash: spi_nor: improve diagnostics/behavior of erase
drivers: flash: spi_nor: improve diagnostics/behavior of erase

Erase can only succeed if the address is sector-aligned, and the span
to erase is an integer multiple of the sector size.  Validate this
before starting the process of erasing things.

Signed-off-by: Peter Bigot <a4112a160b558d5427af084318038e19a95979ee@nordicsemi.no>

nashif/zephyr,nashif/zephyr,nashif/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,Vudentz/zephyr,Vudentz/zephyr,finikorg/zephyr,finikorg/zephyr,Vudentz/zephyr,galak/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,galak/zephyr,nashif/zephyr,Vudentz/zephyr,galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr