Use of Zephyr inbuilt APIs to Use External Flash with nRF9160

I am using MX25 external flash with nRF9160. I am unable to find the configuration to use the Zephyr APIs to access the flash. I am able to access it when I am using 

spi_write_dt funtion but for this I have to do some SPI configuration using the following structs
struct spi_config spi_cfg;
struct spi_cs_control cs_control;
My configuration for Flash in prj.conf

# SPI
CONFIG_SPI=y
CONFIG_SPI_NOR=y

# FLASH
CONFIG_FLASH=y
CONFIG_FLASH_MAP=y
Need some insight on how to use the zephyr-based APIs without doing any other configuration other than DT.
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