mtd: spi-nor: Add support for sst26vf016b

Adds support for sst26vf016b, a smaller variant of the sst26vf064b.
Tested on a sama5d3 SOC using the atmel,at91rm9200-spi controller.
The dual read could not be tested.

SPI_NOR_QUAD_READ is not added because it requires that the IOC bit
from the Configuration Register to be set to 1, which is not the case:
its default value at power-up is zero and we don't set it to one in
spi-nor either.

Signed-off-by: Joseph Kust <joseph.kust@rockwellcollins.com>
Signed-off-by: Brandon Maier <brandon.maier@rockwellcollins.com>
[tudor.ambarus@microchip.com: Drop quad read flag, amend commit description]
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>