mtd: spi-nor: add Spansion S25FL204K support

Spansion S25FL204K is a 4-Mbit 3.0V Serial Flash Memory
with Uniform 4 kB Sectors.

Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
Acked-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>