samples/drivers/spi_flash: fix device naming

There are multiple flash implementations.  This sample was originally
written for the W25QXXDV driver, but has since been used for
jedec,spi-nor.  The sample should work with multiple drivers.

Add device name sources for several drivers, falling back to spi-nor
which was recently used as a test filter.

Signed-off-by: Peter A. Bigot <pab@pabigot.com>