mtd: spi-nor: core: Make spi_nor_set_4byte_addr_mode_brwr public

This method can be retrieved at BFPT parsing time. The method is
described in JESD216 BFPT[SFDP_DWORD(16)], BIT(28) and BIT(20).

Reviewed-by: Michael Walle <michael@walle.cc>
Link: https://lore.kernel.org/r/20230331074606.3559258-6-tudor.ambarus@linaro.org


Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>