RFC: remove w25qxxdv flash driver from Zephyr as of 2.4.0

Peter A. Bigot

The spi_flash_w25qxxdv driver has been superseded by the generic spi_nor driver for over a year. The only non-refactoring change to the W25Q driver in the last 18 months was done to support a backport to 1.14.

All devices supported by spi_flash_w25qxxdv driver are expected to be supported by the spi_nor driver, using the standard jedec,spi-nor devicetree compatible. No in-tree devicetree files make use of this driver.

To reduce confusion about which driver is expected to be used for JEDEC-standard SPI NOR serial flash memories pull request 27802 proposes to remove the redundant driver from Zephyr 2.4.  (It's not practical to deprecate a driver, and the existing one will work only for winbond,w25q16 if anything.

Please raise any concerns you have with this proposal as comments/reviews on the pull request.